The Audi S5 starts with a deep purr, definitely a V8 but refined compared to rumbling Detroit muscle. However, in the upper revs the S5 aligns with the A5 V6's more mechanical song. The gas pedal has lots of travel so the driver can fine tune how much power to apply and how quickly.

Audi's manual transmissions are geared for performance, not highway fuel economy; if long highway cruises are on your agenda the A5 will merrily scoot to 60 mph in about six seconds and easily exceed any speed limit in the world while returning better mileage.

The S5 is an Autobahn bruiser, its elastic well of torque set up to accelerate with authority from virtually any speed (0-60 in less than five seconds) and is still pulling as it is reined in electronically at 155 mph.

That speed isn't useful in the American landscape but the flexibility certainly is. Where some muscle cars reach 50 or 60 mph in first gear with the engine turning 6000 rpm, the freer-revving S5 does only 65 mph in second gear at 7000 rpm. Power comes on smoothly and progressively, with plenty of torque to get you moving and a soundtrack Mozart couldn't better, rather like a muted American LeMans racing sports car, as the engine approaches its redline. At 65 mph, the engine spins 15-percent to 25-percent faster than most big V8s, so even at that speed in top gear there is useful urge in acceleration.

The gearing also pays dividends around town, where motion is so effortless you can start out smoothly from a stop in second gear. The car will idle in gear quite slowly and has decent compression braking so you can crawl along in traffic, and with just the slightest forethought, rarely have to use the clutch pedal. The shifter feels solid and of some heft, reminding us of a front-engine Porsche and heavier than the typical BMW; it is direct, precise and never misses a gear. Indeed, the only negative aspect of driving this car as a daily gridlock grinder is the gas mileage.

At the other end of the spectrum, big brakes and sticky tires haul the car down from speed in a drama-free hurry, without the nose diving to the pavement or the tail standing up like a hound on alert. Designed where repeated heavy slowing from 125 mph is common, the Audi's brakes will be tested in America only on racetracks. Naturally, the latest generations of electronic brake assistants are on board, but you have to be a real poser to have them come into play.

Quattro, Audi's all-wheel drive system that comes standard on the A5 and S5, nominally sends 40 percent of the power to the front wheels and 60 percent to the rear wheels to give dynamics related to a rear-wheel-drive car with the stability and enhanced poor weather traction of all-wheel drive. This system is always on and requires no driver action, automatically distributing propulsion in the most efficient, effective, stable manner.

As a result, the S5 is able to put down all 354 horsepower in any dry conditions and a greater proportion of it inclement conditions than would be possible without quattro. There's no tire spinning nor even a chirp as it lunges toward the horizon. With a set of narrower dedicated winter tires the only alternative that might come close is the considerably more expensive Porsche Carrera 4.

Another large change comes from the S5's layout, the first recent Audi to put the differential in between the engine and the transmission, taking some weight off the front wheels. The S5 splits its weight almost evenly over the front and rear wheels which, when matched with the all-wheel drive, allows each corner to do a near-equal amount of work. That translates to a car that feels less nose-heavy than before, changes directions much more crisply, minimizes body roll (just enough to know you're pushing it) and delivers inspiring confidence; indeed, we covered one stretch of wet road without putting a foot wrong as fast as we'd covered it in dry weather with a top-notch rear-wheel-drive sport sedan still prone to twitching its tail and not because of too much power.

Some credit is due the 19-inch sport tires, but it is the S5's lightweight, independent suspension, good balance, and all-wheel-drive grip that let it put on such displays of composure. Even a hack of a driver can frequently motor along quite briskly without any intervention from the stability system.

The A5 has similar exemplary characteristics; it merely goes down the winding road a bit smoother and slower. Less sticky tires absorb bumps better, as does the more compliant suspension that has no slop or wallow in it.

An A5 with the S-line package is a step firmer than the standard A5, though not as sporting as the S5. The S-line is perhaps the best for enthusiasts saddled with poor roads.

Although the S5 is 150 pounds heavier, with its larger engine and higher feature content, than an A5, the S5 has slightly better balance. The S5 weighs nearly 4,000 pounds, though, and doesn't have quite the feeling of place-it-anywhere lightness of a BMW 3 Series coupe or Jaguar XK. This isn't a bad thing, more a demonstration of the Audi's long-distance, high-speed touring philosophy as opposed to a less-compromised sports car. The ride is never punishing, but those more expensive rides with adjustable suspension do offer a bit more compliance for the marginal surfaces of some interstates.

Steering is nicely weighted and doesn't lack feel or reaction to the slightest turn of the wheel. We classify the Audi's steering heavier than a BMW in standard mode, but lighter than a BMW in Sport mode, so it's a happy medium. At parking speeds, it is light and quick, with a respectable cut for maneuvering.

Adaptive headlights, on models so equipped, swivel to illuminate the road in corners by reacting to steering wheel movement. And these are among the best, as they precisely follow the wheel and don't jerk from side to side as some do, better illuminating the road than making a distracting light show. So we recommend opting for them.