It sounds implausible for the serene Audi A6 to be trans-formed into this fire-breather, but clearly Audi has got fed up playing second fiddle to the BMW M5 in the race to build the most awesome super-saloon in the world.

To cap it all, you can even buy the RS6 in Avant five-door estate form, meaning your labradors are also likely to become the fastest-accelerating dogs in the history of animals.

Inside, a suite of electric leather-covered Recaro seats nuzzles Audi's top line interior spec, while 19in alloys hiding under massively flared arches and aggressive front and rear body styling, make the RS6 visual nirvana.

With an extra 110bhp over the 340bhp S6, you'd expect the RS6 to blow its sibling away on performance – and sure enough it does.

It also dispatches a useful handful of the world's fastest cars, including various Porsches, AMG Mercedes and Alpina BMWs. Even the hallowed M5 has to sit in second place to the RS6's all-conquering torque which, at 413lb ft, puts it into the supercar league.

While top speed is limited to 155mph, Audi is too shy and responsible to brag about the RS6's true maximum without the limiter, though its 0-62mph time of 4.7 seconds is an instant give-away: it went gently unsaid at the car's launch that the test cars were 'delimited' – meaning all 450 horses were up for grabs given a suitable stretch of unrestricted autobahn.

With quattro permanent four-wheel drive, ESP, ABS, massive brakes and a clever adaptive damping system, there was a good chance of living to tell the tale, too. Unsurprisingly, it was not until we were clogging it down the motorway that the delimited experience became starkly apparent.

The rate at which the RS6 accelerates is awesome, all the time accompanied by the V8's hard-edged growl: 100mph turns into a mere dawdle such is the car's stability and refinement. We saw a breathtaking 285kph at one point – about 177mph in English – with more to come.

But in truth the motorway is where the RS6 is at its best – as a mile-pulverising Continent crusher with surprisingly good combined economy of around 19mpg and a fantastic Bose stereo.

Despite its more sporting shift pattern and paddle-operated manual override, the Tiptronic five-speed box feels uncomfortable with the engine's massive output. Sleepy downchanges and a propensity to hunt up and down on part throttle in town is irritating, while a tendency to change up early when you would prefer it to hang on to the lower gears blunts driver enjoyment off the motorway.

Even at £57,700 on-the- road (£58,800 for the Avant), each of the 500 RS6s destined for the UK will still be among the biggest performance bargains around when the first hits the road in September.

Though dynamically the RS6 may not banish the M5 as the greatest driver's car around, it's a certainty that you won't find five seats in anything much faster.