The story used to be that BMW ruled the sport sedan roost, but the all-wheel-drive 2014 Audi S6 is eager to turn the page. With its twin-turbocharged V8, sophisticated air suspension and nimble handling, the light-on-its-feet S6 represents a new direction for Audi. Remember the previous S6? Even with its Lamborghini-sourced V10 engine, it posed little threat to the established order. But the 2014 S6 is the real deal, a super sedan that any automotive enthusiast would feel privileged to own.

Of course, the S6 isn't just an A6 luxury sedan with more motor. For one thing, it comes standard with a seven-speed automated manual transmission that isn't even offered on its lesser-priced relative. For another, its exclusive sport-tuned air suspension magically smoothes out the A6's formerly somewhat busy ride while also improving handling. Then there's the usual assortment of subtle S-model badging and styling cues, not to mention a trick sport differential that can transfer power from one rear wheel to the other. What's more, many of the A6's desirable options come standard here.

Granted, there's a class of sedans that are even more super than the S6. That's where you'll find the BMW M5, for example, which packs an extra 140 horses under the hood. But after a spirited drive in this 420-horsepower Audi, the M5 and its cohorts might lose some of their luster. The S6 is so fast, smooth and responsive that it's hard to imagine wanting anything more. Throw in Audi's superior cabin detailing and cutting-edge infotainment features, and you've got one of the finest four-doors on the planet, bar none.

Entering its second year on the market, the latest Audi S6 does face some formidable rivals, and each starts at a considerably lower price. The 2014 BMW 550i gets a serious power injection this year, though it lacks the S6's sharp handling reflexes. The Jaguar XF Supercharged and 2014 Mercedes-Benz E550 are also compelling European sedans with beefy V8 power. And don't overlook the all-new 2014 Cadillac CTS Vsport, which matches the S6's 420 ponies and makes a fashion statement all its own.

But we think the 2014 Audi S6's elevated price is appropriate, because it feels a little more special than the rest. Imagine that: an Audi showing BMW and company how it's done.

The 2014 Audi S6 is a midsize super sport sedan that comes in a single well-equipped trim level.

Standard features include 19-inch wheels, adaptive xenon headlights with LED running lights, an adaptive air suspension, a sport differential, a sunroof, keyless ignition/entry, heated and auto-dimming sideview mirrors and front and rear parking sensors. Inside you'll find a blind-spot warning system, Audi drive select (providing driver control over steering, suspension and transmission calibrations), diamond-stitched leather upholstery, eight-way power heated front sport seats (with driver lumbar adjustments), a power tilt-and-telescoping steering wheel, driver memory settings, four-zone automatic climate control, Audi's MMI console-mounted electronics controller, an 8-inch display, a rearview camera, a navigation system, Bluetooth phone and audio connectivity, Audi Connect (enhanced Web-based navigation, information and Wi-Fi access) and a 14-speaker Bose audio system with a CD player, HD radio, satellite radio and iPod connectivity.

Options for the S6 are organized in packages. The Innovation package features a head-up display and night vision assist, while the Driver Assistance package adds adaptive cruise control (with stop-and-go functionality), lane-departure warning/keeping, a 360-degree parking camera system and the Audi Pre-Sense Plus collision mitigation system. The Comfort Seating package features multicontour front seats with ventilation and massaging functions, front passenger memory settings, comfort rear seats and leather upholstery sans diamond stitching. The Cold Weather package adds heated rear seats and a heated steering wheel. Finally, the Black Optic package tacks on exclusive 20-inch wheels, body-color exterior mirrors (instead of the standard silver ones), a blacked-out grille and gloss-black window surrounds.

Other stand-alone options include 20-inch wheels, LED headlights, a simulated-suede headliner, rear side airbags and a 15-speaker Bang & Olufsen surround-sound audio system.

The all-wheel-drive S6 is powered by a twin-turbocharged 4.0-liter V8 that pumps out 420 hp and 406 pound-feet of torque. The transmission is a seven-speed automated manual (Audi's S tronic) that drives all four wheels through the standard all-wheel-drive system.

According to Audi, the S6 can blast from zero to 60 mph in just 4.5 seconds. But that's not all: The S6 earns EPA fuel economy ratings of 20 mpg combined (17 mpg city/27 mpg highway). That's an exceptional combination of power and efficiency, particularly for an all-wheel-drive V8 sedan.

Standard safety equipment on the 2014 Audi S6 includes antilock disc brakes, stability control, a blind-spot warning system, front and rear parking sensors, a rearview camera, front seat side airbags, full-length side curtain airbags and front knee airbags.

Rear side airbags and a lane-departure warning/keeping system are optional, as is the Audi Pre-Sense Plus collision mitigation system, which warns the driver and automatically activates the brakes and adjusts the front seats for maximum protection if a crash is deemed imminent.

In government crash tests, the 2014 Audi S6 earned a perfect five-star overall rating across all tests: frontal crash, side crash, and rollover. In crash testing by the Insurance Institute for Highway Safety, the similar A6 on which the S6 is based received the highest possible rating of "Good" in the moderate-overlap frontal-offset, side-impact and roof-strength tests.

Although 420 hp sounds like a lot, the 2014 Audi S6 splits the difference between V8-powered midsize luxury sedans like the BMW 550i and lunatic-fringe members like the M5 and Mercedes-Benz E63. The S6's turbocharged V8 doesn't quite provide supercar acceleration, but it comes close, and the engine's refinement is about as good as it gets. Same goes for the automated manual transmission, which is equally content ripping off perfect rev-matched downshifts or just trundling around town.

On the handling front, the S6 approaches sports car territory with its quick steering and tenacious grip, yet the standard air suspension keeps the ride civilized on all surfaces. There are cars that do certain things better than the S6, but very few can match this Audi's all-around excellence.

In keeping with Audi tradition, the 2014 Audi S6 has one of the nicest cabins in its class, highlighted by a handsome dashboard layout, top-notch materials quality and solid fit and finish. The standard Multi Media Interface system (MMI) controls entertainment, communication and navigation functions via a dash-mounted pop-up screen and a knob and buttons on the center console. The system boasts logical menus, crisp graphics and a touchpad to increase functionality, although we still prefer BMW's iDrive or Mercedes' COMAND for overall ease of use.

The S6 also features the Audi Connect Internet suite, which includes in-car 3G WiFi, Google Earth data for the navigation system and simplified Google search for POIs. It sounds a bit over the top, but proves very handy if you need to get some work done on the road and there's no Starbucks in sight. However, the Google Earth feature is an example of form over function, as the "enhanced" map can be more difficult to comprehend at a glance than a conventional navigation map.

Whether you keep the standard sport seats or opt for the multicontour comfort seats, we're confident that you'll find them supportive during long trips and spirited back-road runs alike. As for the S6's trunk, its 14.1-cubic-foot volume is on the small side for this segment, though the split rear seatbacks fold down and offer a pass-through feature for longer objects.