BMW went and did it. After constantly improving the current 5 Series platform until it was one of the best sport sedans on the planet, they've taken the segment to an entirely new level with the radical M5. If you're already a fan of the 540i, prepare to be mesmerized by Bavaria's top performance sedan.

Starting with the 4.4-liter block from the 540i, BMW's M Division bumped displacement to 5.0 liters with a bore and stroke job. Compression is set at 11:1 (requiring the use of premium fuel, of course) and the cylinder heads are redesigned to offer greater crossflow cooling. Outfitted with the requisite double-VANOS variable valve-timing system, this engine is good for 394 horsepower. Even with the M5's 3,800-pound curb weight, zero-to-60 acceleration happens in a lightning-quick 5 seconds! But don't expect those times to happen with both hands on the wheel; the M5's only transmission is a six-speed manual.

Along with Corvette-like acceleration, the sedan features a lower ride height than you'll see on a standard 540i, aluminum suspension pieces, stiffer spring and shock rates, and 18-inch wheels with Z-rated tires. A sport mode switch on the center console will recalibrate the variable-assist power steering for increased road feel and snappier throttle response. When things get too snappy, traction control and electronic stability control are waiting to intervene (unless you've switched them off).

While paying 70 large for a performance toy might not sit well with the other half, don't forget to mention all the amenities that come standard on every M5 Sedan. Dual-zone climate control, heated leather seats with leather inserts and eight-way power adjustments, power headrests, a GPS navigation system, a 10-speaker sound system, one-touch power windows, rain-sensing wipers, etc., etc. Remember, you're not just buying a European hot rod, this car is meant for safe and secure family transportation...right?

You can customize the interior look of your M5 with a slew of no-cost options. Prefer the Nappa Heritage leather to the Nappa Point leather or the bruyere Wood Trim to the burl Wood Trim? Just check the option boxes that appeal to you. You can even delete the rear spoiler to further hide your M5's true intentions. Park Distance Control, a rear sunshade and a rear-seat pass-thru are the only extra-cost factory options, though a BMW CD changer is pre-wired and can be dealer installed for a nominal fee.

The M5 represents BMW's most capable performance car yet. It is an uncompromising sport sedan in terms of both ability and amenity. If your demands for horsepower, handling, hedonism and hip-room run to the extreme, the M5 has no peer.