Audi RS6

Based loosely on the potent 4.2-litre S6, the 450bhp RS6 quattro Avant is billed as a genuine supercar and the pinnacle of the A6 range. To help distinguish it from lesser A6 models, Audi has fitted subtle RS6 badging to the hand-built machine, as well as deep bumpers complete with mesh grilles.

Huge 19-inch wheels fill the arches, while at the rear there are two oval exhaust pipes. Inside, there's a distinctive interior, offering optional carbon fibre trim and RS6-embossed seats. A saloon edition will also be available, although this is not expected to be as popular as its more practical brother.

Whatever the bodystyle, there can be no doubting Audi's enthusiasm for its latest high-performance flagship. Factory engineers have complete confidence in the newcomer's abilities - even when compared with some of the world's most desirable machinery. They single out BMW's 400bhp M5 and the Mercedes AMG E55 as direct rivals, but claim that the RS6's potent twin-turbocharged engine has the ability to leave both challengers trailing.

As the V8 powerplant rumbles into life, it's not difficult to understand why. The engine has one of the most distinctive growls we've heard, and revs quickly and keenly for a unit that relies on turbos to supply its urge.

To ensure reliability, Audi has been forced to fit the robust yet slick-shifting five-speed Tiptronic gearbox developed for the A8 W12, rather than the six- ratio unit which is shared by the rest of the A6 range. However, the loss of sixth gear is not a problem, because the RS6's 560Nm of torque is more than capable of propelling this estate towards the horizon at an astonishing pace. In fact, you virtually have to recalibrate all your senses just to keep pace of the distances the RS6 will cover - even on a narrow throttle opening. Official figures show that the all-wheel-drive machine sprints from 0-60mph in only 4.9 seconds. And unbelievable as it may seem, the acceleration beyond this point feels even stronger. The experience is also enhanced by the fact that wind noise in the cabin is nearly non-existent, even at Autobahn cruising speeds.

As with its rivals, the RS6 feels rock-solid on motorways, but the great-est surprise is the suspension system. Criticisms about the harsh ride of previous sporty Audis have been taken seriously, and the new model is a major step forward in terms of the car's poise, ride refinement and stability.

That said, the newcomer is not without flaws. The steering still feels slightly numb, and although it proves precise and well weighted, turning into corners at high speed leaves the driver wanting rather more information about grip levels. The brakes, however, are simply sensational. Thanks to the use of eight-pot calipers, which are more usually reserved for Le Mans-style race cars, the ABS and ESP-backed set-up is powerful and incredibly consistent. As a result, the RS6 proves to be the best driver's machine that Audi has built since it put the finishing touches to the original Quattro in 1980.

With this in mind, it's a shame that only 500 cars will be imported to the UK during the next two years, priced at £57,700 for the saloon and £58,800 for the Avant. Whatever the numbers, Audi has built a model with the credentials to rival the likes of BMW's M Division and Mercedes' AMG. So at group test time, we may find the opposition has been hit for six!