Road Test: Land Rover Range Rover Sport 5.0 Overfinch GTS-X 5dr Auto

It is a lazy stereotype that all Premiership footballers drive modified Range Rovers. Unfortunately, it's a lazy stereotype that's largely true, particularly in the case of Overfinch-tuned Range Rovers. At one point during Euro 2012 (a man from Overfinch admits) seven of the 11 England players on the pitch were Overfinch owners. This makes them more popular among top English footballers than Cristal fizz, extramarital dalliance and missing penalties.

And no Overfinch will be more popular with the Champions League crowd than this, the new GTS-X. What we have here, in simple terms, is Wazza's favourite Range Rover Sport V8 with a chunk of extra power, dropped suspension, big kerbable alloys, orange paint... and a price tag just short of £150k (a standard RRS V8, by comparison, starts at £70k). One hundred and fifty thousand pounds! Why, for some footballers that represents six hours of hard work!

However. Perhaps conscious that - bar a bit of transfer-window activity each season - the Premiership market is a finite one, Overfinch is keen to expand beyond footballdom. Under new ownership since 2010 and now based near Leeds, Overfinch considers itself a classier proposition than Britain's myriad other RR tuners, and is keen to prove it can do upmarket, bespoke and tasteful, as well as, er, Terry-spec.

Which is why, when you heave open the door of the GTS-X, you're confronted not by diamanté-encrusted ostrich leather and crystal disco-chandeliers, but a surprisingly restrained patchwork of black nappa leather and neat carbon-leather weave. All very sympathetic, as are the mechanical upgrades: traditionally Overfinch hotted up its Range Rovers by stuffing them with V8 Corvette engines, but nowadays its strategy is subtler. The GTS-X retains the Range Rover Sport's 5.0-litre supercharged V8, but gains an ECU remap, upgraded induction system and an ear-assaulting sports exhaust to boost power from 500bhp to 575bhp. Overfinch says that, "on a good day", the GTS-X will crack the 0-62mph sprint in five seconds, a scary stat for something tipping the scales at two-and-a-half tonnes.

The performance is as alarming on the road as it is on paper. Like a V8 RRS but more so, the GTS-X is (a) preposterously fast and (b) tainted with the suspicion that something so heavy shouldn't be hustled at such speed. The GTS-X's suspension is notably firmer than the standard RRS's, meaning that, though it can't sponge up nasty surfaces quite as elegantly, it stays even flatter through corners. The uprated Brembo brakes are devastatingly effective.

The exhaust is worth a sizeable chunk of the entry fee on its own, firing off a barrage of subterranean detonations beneath the car. You can turn off the noisiest of the burbles and booms via a switch in the centre console but, unless you've been issued with an ASBO for disturbing the neighbourhood peace, you won't.

But more than the alarming pace and noise, it's the interior fit and finish that gets you. Overfinch works its magic on every visible surface of the RRS's cabin: even the far edges of the A-pillars, the sides you'd only see if you pressed your face right up against the inside of the windscreen, are immaculately trimmed. I didn't get a moment alone to lick the supple leather upholstery but suspect that, if I had, it would have tasted of rare fillet steak. Bespoke is big at the moment, and this is pretty much as well-executed as bespoke gets: immaculately upholstered, with not a crease nor squeak to ruin the expensive craftsmanship.

Talking of ruin, it rather depends how you spec your GTS-X. If you so desired, you could have every one of the seats' many-dozen little leather panels in a different colour. Overfinch hit the headlines a few years ago for providing former Manchester City footballer Stephen Ireland with a particularly tasteless pink-on-white Range Rover. Though Overfinch says Mr Ireland made his own post-delivery ‘modifications' to the car, it accepts that it'll do its best to accommodate requests.

"If someone comes to us asking for a really outrageous colour combination," says the man from Overfinch, "we'll do it, but we wouldn't necessarily put it on our website."

Let's not be too sanctimonious here. Any company with a vague desire to remain in profit would be daft to wave away a queue of millionaires with open chequebooks. And, hey, you can't really blame John Logie Baird for Keeping Up With The Kardashians, can you?

Currently, Overfinch sells a couple of hundred complete cars annually (as well as ‘upgrading' several hundred more Range Rovers to Overfinch spec), but will soon offer a hotted-up Evoque and Defender, as well as its own take on the all-new Range Rover. Overfinch describes its current relationship with Land Rover as ‘arm's length', but says it would love to become LR's in-house tuner, as AMG is to the Mercedes mothership.

Does the GTS-X show sufficient promise to achieve this lofty aim? We'd say so. Yes, £147,500 is a mad sum of money for a modest power upgrade, a body kit and some tasty leather (though if you're happy to forgo the extra power, the posh brakes and suspension upgrades, making do instead with the standard RRS's entirely sufficient 500bhp output and mechanicals, you can have all the visual impact of the GTS-X for a rather more reasonable £90k or so). But the Overfinch is stunningly finished, far more coachbuilder-chic than eBay add-on. If you want to royally ruin yours with a lime-green-on-burgundy velour colour scheme, Jermaine, don't say we didn't warn you...