Mercedes E63 AMG versus Audi RS6

155mph. That's - shoes and socks off, carry the one - 70 metres a second? Forty-odd football pitches a minute. As our pair of estates boom through the Munich night on the deserted, derestricted autobahn, a profound thought occurs: if my dodgy maths is correct, 155mph is Really Quite Fast Indeed. Turbos shriek, exhausts thump, 1,100bhp detonates into the darkness. The Audi RS6 and Mercedes-Benz E63 charge east in unison, and another profound thought strikes home. Downsizing: not the end of the world, is it?

Downsizing. The word feels comically out of place when vmaxing a 550bhp twin-turbo V8 family estate on the fastest public roads in the world, another twin-turbo, V8 family estate hot on its heels. But deep, deep beneath the surface, these two bruisers are tofu-waving green revolutionaries. Really. The new RS6 has shed 100kg, is more economical and - leading to unprecedented scenes at the German Horsepower Society - less powerful than the car it replaces, trading its predecessor's V10 for an Audi-tuned version of the twin-turbo V8 doing sterling service in the Bentley Conti GT.

A V8 that - thanks to clever shutdown tech - becomes a four-cylinder under light load, no less. Merc's AMG division hasn't gone quite so yoghurt-weaving. But its new E63 - though more potent than its precursor - also chases improved economy and emissions through the mysterious alchemy of turbocharging, a move that must've caused some soul-searching at the world's foremost exponents of swept-capacity, naturally aspirated lunacy. The old 6.2-litre atmospheric V8 is gone, replaced by a 5.5-litre bi-turbo unit some 32bhp more powerful. Which makes our two estates spookily closely matched: the Audi produces 553bhp to the Merc's 550, but 15lb ft less than the AMG's 531 torques. Both will officially return 28mpg and under 240g/km of CO2. It won't get either manufacturer onto Al Gore's Christmas card list, but it's a start.

But while they follow a similar recipe for making their power, the two Germans stand on either side of a great philosophical - nay, moral - divide, perhaps the greatest schism facing humanity today. And that quandary is this: two or four? The RS6, as with all hot Audis, remains four-wheel-drive (though admittedly a rather trick four-wheel drive, with torque-vectoring, a crown centre diff and rear differential), while the E63 chucks its power to the rear wheels alone. It's a distinction that defines these two cars, one that represents the biggest rift in the world of performance cars today.

So, as George Orwell never had it, is it 2WD good, 4WD better... or vice versa? Well, if it's Top Trumps victory you need, 4WD's for you. With its traction advantage, the RS6's official 0-62mph time is 3.9 seconds. Under four seconds. In a nearly-two-tonne family estate. That's as fast as the Ferrari F40 ever managed. And you know what? It feels it. Nothing short of an Ariel Atom can rival the RS6 for reducing you to a cackling maniac as you plant the throttle and try your feeble best to wrap your faculties around the sensory overload enveloping you. Difference is, where the Atom experience eases up as you hit triple figures - metered by aerodynamics and your own desire not to become an integral part of the scenery - the RS6 just keeps pulling and pulling at the same ludicrous rate, all the way to 189mph if you remove the limiters, which you will. There's not much on this planet to make an E63 seem a bit pedestrian, but the Merc can't match the RS6 for Mein-Gott-this-feels-schnell acceleration.

There's also not much else on the planet that makes B-road overtaking so dismissively simple as the RS6. Gap-throttle-done. Gap-throttle-done. Repeat until all traffic is vanquished. Even on damp roads caked in gravel and cow dung and fallen leaves, the RS6 gets from A to B, C, D and the rest of the alphabet at absurd pace. No matter what speed and what corner, no matter whether you slam on the brakes or stab the throttle, somehow the Audi's array of differentials and electronic trickery sorts it out. It's a car that instils great reserves of misplaced confidence, the belief you can head into any bend at any pace and emerge intact, confidence that may evaporate the day you find yourself entering a blind hairpin at triple-figure speed and, shortly thereafter, airborne somewhere over Dunkirk. Physics can only be bent so far.

The E63 is far readier to remind you that you are a pitiful, flawed human being. In the dry, traction levels are prodigious - thank a combination of fat rubber and smart stability control - but show the Merc a greasy, gravelly road, and you're suddenly very aware of the limitations imposed by the laws of friction on any efforts to smuggle 550bhp to the road through just two wheels. Treat the traction control buttons with the respect they deserve, and the E63 will do everything in its power to keep you out of danger, but take liberties, and, like an East End hardman, it'll teach you a lesson in manners.

The reward for this in-yer-face demeanour is a far keener, more involving drive if you're prepared to offer the Merc your full attention. Where you simply point the RS6 at the middle of a corner and, once you're there, point it at the exit - brakes and/or throttle optional at any point - the Merc, as the racing community would have it, gives you options, allowing you to subtly adjust your angle of attack mid-corner on the throttle. In reality, this may mean adjusting your angle of attack mid-corner from ‘on the road' to ‘in a hedge'. Still, the E is a mighty tactile thing for a five-metre barge. Even its gearshift paddles - great metal levers that produce a reaction a touch slower than we'd really like - feel more analogue than the RS6's tiny plastic flickers, which wouldn't seem out of place on a PlayStation controller.

Actually, that's exactly how the Audi feels: like a very fine computer simulation of itself. Partly because it imbues you with an air of detached immortality on the road, but also because of the odd remoteness of its controls, not least its ropey steering. Yes, the RS6's rack is mighty quick, sending the Audi's nose pinging towards corners with frantic fervour, but it seems to be connected to the front wheels by a series of intensely powerful but intensely rubbery rubber bands. Switching from hyper-assisted, falsely weighted Dynamic mode into the Audi's Comfort setting helps a little, but it still feels closer to the world of console gaming than one of the most exotic super-estates on the planet.

The E steers beautifully, the sensation aided by its spot-on Alcantara-trimmed wheel, which is slim and precise and a welcome departure from the fat-stuffed rims so in vogue. Its calibration is a thing of subtle delight: light and quick but still feelsome. It feels deeply, mechanically right, a solidity echoed in the noise department. The E63 makes all its best noise down the bottom end of the rev range, churning out a great baritone choir of booms and detonations, a battlefield salvo seemingly occurring several miles off.

The RS6 - with £1,000 sports exhaust, which should be the very first option box you tick - can't quite match the Mercedes for low-revs bassline, but makes up for it with a bonkers air-bullying soundtrack in the midrange, snorting its way to 5,000rpm like a brace of industrial vacuum cleaners battling to the death, and snap-cracking on the overrun with enough volume to reduce any toddlers within a five-mile vicinity to tears. So disconcertingly violent is the RS6's exhaust, in fact, that you occasionally find yourself wondering if the rear diff has splintered straight through the bootfloor.

There's more than a little, ahem, cosmetic enhancement to the Audi's aurals. Open the door (when stationary, preferably), rev the engine and you'll find a chunk of the noise has mysteriously disappeared, an indication of just how much of that sound is of less than organic origin. An editing trick it may be, but it's a mighty effective one.

The Disney soundtrack matches the Audi's more extravagant visuals, too. In the utterly unstealthy ‘stealth' grey paint of our test car, between the anabolic arches, the giant wheels and the ‘quattro' branding smeared across every available surface, the RS6 isn't the hyper-estate for the driver who likes to make his 550bhp, 189mph progress in anonymous fashion. The E, despite its huge new pair of nostrils and quad tailpipes, rocks the hot estate Q-car vibe far more than the Audi.

It's a purer piece of mechanical engineering, the AMG, and feels more likely to be barrelling around in 50 years' time, doubtless in the hands of a fuel-bankrupt but perma-grinning Munich cabbie. Take it gently, and the Merc is an easier car to live with day-to-day: it's quieter on the autobahn, with far less road noise, though our Audi's bigger wheels - optional 21s while the Merc rolls on standard 19s - play a part in that. In Germany at least, it'll ferry more humans: where the E63's rear bench seats three, the RS6 gets two ‘sports' seats in the back. British RS6s will be full-fat five-seaters as standard.

But who bought a V8 super-estate for going slowly? Flat-out, head-to-head with the RS6, the Merc's lovely steering and sheer mechanical rightness probably cancel out its slower gearbox and more muted exhaust. So it all comes down to that big question: 4WD security or 2WD tactility?

The apex-clipping racing driver inside each of us screams rear-drive, of course. But these are giant estate cars, not track-day specials. I will wager strongly there are more people in Britain who sculpt confectionery mannequins of Richard Hammond than thrang their E63 or RS6 estates around a circuit on any given Sunday. If you want a feelsome sports-thing for the track, buy a proper one for half the price. The real world doesn't have sticky tarmac and gravel traps, and behind its veneer of smart chassis dynamics and idiotproof software, the E63 is a chunky estate that shoves nearly twice the power of a WRC car through its back wheels. Even on the finest set of winter tyres, I don't think I'd fancy it in the snow. Living in Britain, with its rain, frosts, manure-splattered back roads and dodgy tarmac, quattro's what you want.

So here's your TG Top Tip: swallow your Senna-shaped pride, and go 4WD. Which doesn't necessarily discount the E63, because, for the first time in history - and perhaps in tacit admission that most drivers need all the traction they can get - Mercedes is now offering its super-estate in four-wheel-drive flavour. But only if you're happy with your steering wheel on the wrong side: Merc doesn't engineer the 4Matic E63 for right-hand drive. Until it does - and unless you're really, really as good as you think you are - the shouty, show-off, surprisingly safe Audi is the car for Britain.

But right now, out on Munich's big, dry, empty autobahn, the two-versus-four schism is irrelevant. All that matters here is brute power, and both our estates are using every last ounce of theirs as they whip through the Bavarian night towards Austria. If you spend your life driving in stultifying, 70mph speed-limited Britain, being set loose on a derestricted 'bahn feels... wrong, really. Initially, you tiptoe your way past 100mph, peering out guiltily for the first sign of a traffic cop, convincing yourself there's no way, legally, such velocity should be allowed. And then a dowdy VW Passat - because it's always a VW Passat - whumps past in the outside lane and (provided your car and the road conditions are suitable, obviously) you think, "Well, if he's doing it, it'd be rude not to join in." Jeez, distances vanish quickly when you're doing two and a half miles a minute. Countries become significantly smaller; life becomes significantly better.

One day, the autobahns may be gone. Just this month, the leader of the German opposition party threatened to slap a 75mph limit on all of his country's motorways if he gets into power. Here's hoping he doesn't. Where else but Germany, and its unique, derestricted roads, could produce brilliant, daft cars like the RS6 and E63? Downsize the engines all you like, but don't downsize our autobahns...

Pictures: Thomas Salt 

This feature first appeared in Top Gear magazine