Equipped with Audi's quattro variable all-wheel-drive system, the RS5 starts off with a 40/60 front-to-rear torque split but can shift power fore and aft as surface conditions dictate, and its rear sport differential provides torque vectoring in corners to help the car turn.

The quattro all-wheel-drive system provides sure-footed agility. (Photo: Audi)

The Drive Select system dishes up various chassis and steering calibrations to broaden the car's bandwidth and, when equipped with the optional MMI telematics interface, will allow individual tuning of throttle response, transmission shift points, steering-assist levels, the sport differential and the exhaust, which has internal flaps to reduce noise.

Wave-profile rotors make their first appearance on an Audi with the RS5, coincidentally at the moment the company announces its acquisition of Ducati. Wave-contour rotors are used to reduce mass and are common on motorcycles. Even lighter ceramic brakes are optional.

Other changes to the exterior of the RS5 include oval exhaust outlets flanking the larger rear diffuser. Above that, the active tail spoiler pops up at 75 mph and snaps down again at 50 mph. The car is offered with 19-inch wheels standard, but our test cars were equipped with beautiful 20-inchers, available as an option.

Inside the car, you find the flat-bottomed RS5 steering wheel, elegant split-style door handles and firmly bolstered sport seats. Optional equipment includes Audi Connect (which allows Wi-Fi hookup to eight devices), a Bang & Olufsen audio system, backup camera and Google Earth navigation graphics with new (to cars) Street View.

An active tail spoiler lifts at 75 mph and snaps back down at 50 mph. (Photo: Audi)

Multiple-personality operation has become de rigueur in high-end sport sedans and coupes, and this car is no exception. We crept through heavy San Francisco traffic and cruised its freeways in luxurious comfort, then circulated the undulating contours of Sonoma Raceway, where the RS5 deploys all its high-performance credentials to good effect.

With its Drive Select system switched to dynamic mode, the car corners with little roll or pitch, yet it turns in well and even rotates when trail braked enthusiastically into corners. A little steady throttle helps stabilize the car through Sonoma Raceway's tricky downhill esses as the rear axle overdrives its outer wheel to generate yaw.

Even with the steel brakes, the car stops pretty well for a two-tonner, and we did not experience any fade. Best of all is the stirring thunder from the exhaust at full power and the brief burps as the injection cuts during gearshifts. It's not hard to feel Audi's motorsport pedigree in the car's responses because the handling balance is a great compromise between stability and responsiveness.

Still, we need to remember that this is a heavy street car and when driven by professional race-car drivers on the track will not allow very late trail braking into corners without becoming unsettled. No one else will have much to complain about.

Naturally, with 450 horsepower, its straight-line performance is, shall we say, more than strictly necessary for the commuter life it will likely lead. In the real world, the only glitches we noticed were the sometimes magnetic feel of the electromechanical power steering and an occasional abrupt downshift while we were rolling to a halt. And the transmission once declutched during a long uphill stop-and-start sequence, allowing the car to roll backward.

But it's an indulgent ride in every way, and if this car meets your needs on paper, it will very likely fulfill them on the road. At nearly $70,000, it isn't cheap. But it doesn't shortchange the driver in any way. Fast, handsome and capable, the RS5 is rolling confirmation of Audi's rising role in the automotive realm.

This story originally appeared at Autoweek.com