Road Test: Audi A6 3.0 BiTDI Quattro 313 S Line 5dr Tip Auto

The 313bhp bi-turbo diesel A6 Avant will hit 62mph in 5.3 seconds. For all the astonishing supercar stats you'll find in our Stelvio showdown from issue 221, that one might be even more quietly staggering. Five point three! From a chunky estate with a modest-capacity diesel engine! Not an ‘RS' or even an ‘S' badge in sight! Consider us officially boggled.

And, with the 3.0-litre V6's twin turbos working sequentially to provide a seamless swell of power, the A6 feels even quicker than 5.3 in day-to-day, open-road driving. With 479lb ft of juicy torque (more than a Ferrari 599 GTO, no less) slopped right across the rev range, you simply vanquish lines of dawdling traffic with a dismissive wave of the hand and a Bond-villain cackle. Fear my torque, underlings!

The V6's stats eclipse even BMW's diesel flagship, the 535d, generating an extra 14bhp and 37lb ft despite near-identical economy and emissions. When worked hard, it doesn't feel quite as free-revving as the BMW straight-six, but Audi engineers put this down to their car's long gearing - the überdiesel A6 uses an eight-speed Tiptronic transmission calibrated for economy. We'll have to get the two Germans head-to-head to tell for sure.

Thankfully, the car wrapped round this monstrous engine manages to do it justice. Big Audis always seem to make more sense as estates, and that rule holds here. Though the A6 Avant's angled rear (a rear with more than a whiff of Ibiza Sport Tourer to it) compromises bootspace for large cuboid objects - fridge freezers, say, or rhino coffins - it lends the estate a more distinctive appearance than the amnesia-inducing A6 saloon.

Even with its sportback profile, the Avant's bootspace is virtually identical to the BMW 5-Series Touring, though at 565 litres with the rear seats up, it's 130 litres short of the chasmal E-Class Estate. Then again, the Audi is 200kg lighter than the equivalent E, so what you lose on the bootspace swings, you gain on the kerbweight roundabout.

Those fond of their driving licence will be pleased to hear the Avant comes in a range of more sensible engine flavours, including an entry-level 2.0-litre diesel with 175bhp. With any engine, the A6 is a decent drive. Admittedly, it doesn't cope with pimply roads quite as serenely as the E-Class, but it's a huge improvement on Audis of old, with a far more supple secondary ride. With four-wheel drive, grip is mighty, while the steering - if you're into that sort of fetishistic stuff - is pleasingly weighty, if short of feel.

You can even spec your Avant with Audi's ‘Hands Free Boot Operating System', allowing you to pop the tailgate by simply aiming a kick in the direction of the rear bumper. At least, that's the theory. The system seemed unimpressed with TopGear's best foot-waggling attempts, making us shake it all about for a good 10 seconds before opening up. Apparently, we were doing it too slowly. We'll leave the fast-boot expertise to Audi.