The E350's V-6 wants to be revved to deliver, so you find yourself frequently in the 4500-to-7000-rpm bracket. The accelerator pedal's long travel and the seven-speed gearbox's velvety-smooth pickup make this engine feel less quick than the factory figures suggest (0 to 62 mph in 6.8 seconds). As far as high-velocity NVH is concerned, the Merc has a slight edge thanks to its more relaxed gearing.
Although the 530i will sprint to 62 mph in a competitive 6.5 seconds (the U.S.-spec 528i takes more than seven seconds), its peak torque doesn't provide as much midrange muscle as its challengers. The smooth-running straight six is mated to an overly nervous six-speed automatic that sometimes changes gears just for the sake of it. Pushing the sport button triggers an even more hectic calibration that loves chasing ratios even at autobahn speeds.
The A6 rewards you with an extra portion of bottom-end grunt and a large helping of top-end urge. Most of the action happens between 2000 and 5000 rpm, when the plentiful torque provides a kick big enough to make you smile. At 5.9 seconds, the Audi is the quickest to 62 mph, and it extends this lead all the way to the 125-mph mark.
Only the A6 comes standard with four-wheel drive, which is typically a pricey option at BMW and Mercedes. Quattro is an asset, offering unrivaled bad-weather traction plus a very high standard of stability. Through corners fast or slow, the Audi never feels quite as big and heavy as it is. Even on undulating pavement, the nose-heavy sedan (58 percent of the curb weight rests on the front wheels) retains its stoic determination and stays on course. The variable-rate Servotronic steering is on the light side, but it is accurate and quick. At the limit, there's no steering fight and very little protest from the chassis. Its excellent brakes are attentive, progressive, strong, and have excellent stamina.
Although our test car was equipped with an optional sport suspension, the 5-series is more tolerant of imperfect road surfaces than the Audi. The BMW feels firm and sporty, but it doesn't sacrifice the last inch of suspension travel to the god of roadholding. Unfortunately, this suspension setup is offset somewhat by the optional active steering system. Even after almost 500 miles, synchronizing the steering angle with the radius of a corner and timing steering inputs in relation to vehicle speed were difficult. We would prefer a more linear and progressive setup, with a less frenetic response. Luckily, active steering is a stand-alone option in the United States.