IF you don't think a mere 155mph is quite quick enough in your new Audi RS 3 you can go faster still - at a price.

Hand over a princely £1,600 and someone on the production line in Audi's new sporting cars factory in Germany will unlock its whole 174mph potential.

That simple electronic upgrade costs £1,600 but does buy bragging rights in the pub. You'd be mad to approach the limit, even on a derestricted stretch of dry, traffic free autobahn, of course.

On a streaming wet British blacktop with too many lorries in the way, something approaching half the theoretical maximum was asking for trouble (and a felt collar, probably).

So the new and ultra fast Audi needed to impress in other ways on its test drive. For instance, the way this latest version of the company's smallest RS range puts its 400 horsepower down on the road, wet or dry.

That output makes it the world's most powerful five-cylinder engine, its 2,480cc capacity boosted by a turbocharger and kept reliable, light and revvy with expensive tech like a magnesium sump, aluminium crankcase, plasma coated cylinders and a crankshaft that's hollowed out to save weight.

All pricey things to do on a car destined to sell in thousands around the world - and expected to top the 1,298 examples of the old car sold in the UK last year.

Part of the anticipated volume hike comes from the availability of an RS 3 Saloon for the first time. Partnering the RS 3 Sportback five-door hatch, it costs £45,250 against the hatch's £44,300 but despite the £950 extra it's expected to take 40 per cent of sales.

It must be because it looks even cooler than the hatch and especially potent in £550 worth of Daytona grey pearl effect paint with big titanium coloured 19in alloys adding another £695.

It won't be because the saloon is the more practical people mover. Its luggage capacity can't match the hatch, with 315 litres of boot space (770 with the rear seat folded) against the 335 and vastly greater 1,175 litres of the hatchback.

Either shaped RS 3 will hit 62mph in a mere 4.1 seconds, helped by the traction that comes with quattro all-wheel drive. It is always pushing power to both ends of the car but an electronic brain can adjust the mix in microseconds if one axle starts to lose grip.

On the drenched roads of the test drive this ability counted for much more than that 174mph flat out figure.

This feeling of planted security even under power was nicely enhanced by a ride that while sporting (the RS 3 is an inch lower than other A3 derivatives) is never jarring, especially when left to decide how firm to be.

A twist and push of a control knob between the front seats can turn things hard, but you'd want a race track (or German autobahn surface) to benefit much from that.

This new RS 3 costs a chunky £3,505 more than the last one but you get more kit for your money, to soften the blow.

There's more power, for starters, up 33 horses and better acceleration as a result, shaving 0.2 seconds from the 0-62mph time (now 4.3 seconds). The time to 124mph is down from 15.8 seconds to 14.3 seconds, which is quicker than a Ford Ka+ takes to reach 62mph...

Official fuel consumption is actually worse than before, at 34.0mpg (versus 34.9mpg) although the 31.6mpg achieved on the wet-roaded test drive may be more realistic. Either figure is unlikely to trouble someone hell bent on RS 3 ownership.

Proud owners won't care much either about a CO2 figure of 188g/km that means an £800 road tax hit the first year and a BIK of 36 per cent if the car is run on the business's books.

Much more important will be the way the gears slip through in the seven-speed automatic gearbox. Click round to sport setting and the change become even more eager; add £1,000 worth of sports exhaust system and the five-cylinder throb from the engine could turn addictive.

You don't pay extra on the new RS 3 for Audi's virtual cockpit display that turns the instrument panel into a wide television screen that can display the (standard fit) satellite navigation in clear view.

Also standard are front sports seats (although, being Audi, lots of buyers will find £795 for an even sportier look to park themselves on), along with LED headlights and those rear indicators that pulse out a line of orange and will impress following drivers no end.

Audi's thorough detailing on this very fast car extends past gently massaged front and rear tracks sitting under widened wheel arches at the front, to bigger brakes, dual branch exhaust and discreet RS body bits, leading on special bumpers and high gloss black for the radiator grille.

It all helps a fast car to earn its place on roads where going not very fast at all is likely to be the RS 3's default setting.