The new 2010 BMW X6 M performance crossover is the sort of vehicle that's hard to figure on paper. A 555-horsepower twin-turbo V8, hatchback body style, SUV ride height, four seats, limited hauling capability -- it all sounds like a recipe for irrelevance. Yet the X6 M wears the distinctive "M" badge of BMW's Motorsport division, and that's something BMW doesn't take lightly. Purists may scoff at the presence of not one but two SUVs in this exclusive ultra-performance club (the mechanically identical X5 M is also new this year), but one drive in the X6 M should be enough to convince you that it's a worthy member.

Why? Two simple reasons. First, it's really fast. Along with the 555 hp, there's 501 pound-feet of torque from the V8 to motivate this 2.5-ton vehicle. In fact, those 555 horses are 5 more than the gonzo Porsche Cayenne Turbo S can manage, and the Porsche's no lightweight either. A sprint between the two is likely to be a wash -- no small accomplishment for the X6 M given that it costs about $35,000 less.

Second, its handling capabilities are like those of a sport sedan. Standard 20-inch performance tires and a special sport-tuned adaptive suspension certainly help, but a lot of crossovers have such features these days. The X6 M's trump card here is what BMW calls "Dynamic Performance Control," a sophisticated torque distribution system that works in conjunction with all-wheel drive to apportion power to aid traction as well as overall handling balance.

On the downside, the X6 M is one of the least versatile crossover SUVs we've tested. Maximum cargo capacity is only marginally more than you'll find in some economy hatchbacks. There's room for just four occupants, so you can forget about carrying a fifth person in a pinch. At least the V8's 501 lb-ft of torque yields a healthy maximum tow rating of 6,600 pounds. Still, that's about the only practical feature that gives the X6 M an edge over, say, the five-passenger M5 sedan. More to the point, its X5 M sibling offers the same performance along with superior practicality.

But let's be honest -- a vehicle like this isn't about practicality at all. It's about passion, performance and individual expression. In this sense, the 2010 BMW X6 M actually isn't a bad fit with the BMW M tradition. Its rivals certainly deserve close looks, including the various V8-powered Porsche Cayenne models, the Mercedes-Benz ML63 AMG, BMW's own X5 M and the much cheaper Infiniti FX50. But the X6 M is one of the most capable and unconventional crossovers ever produced, and for some well-heeled buyers, that's likely to be enough.

The 2010 BMW X6 M is a four-passenger ultrahigh-performance luxury crossover SUV. As you'd expect at this lofty price point, standard equipment is ample, including 20-inch alloy wheels with summer performance tires, a self-leveling electronically adjustable active suspension with M-specific sport tuning, headlight washers, front and rear parking sensors, xenon headlamps, a power liftgate, a panoramic sunroof, auto-dimming mirrors, leather upholstery, eight-way power heated front sport seats, a sport steering wheel, ambient interior lighting, dual-zone automatic climate control, Bluetooth, a 12-speaker CD/MP3 stereo, the latest version of iDrive with more physical buttons and a redesigned menu structure, and a hard-drive-based navigation system with real-time traffic.

Options include soft-close automatic doors, ventilated "multicontour" seats, heated steering wheel and rear seats, a rearview camera, a head-up display, a six-DVD changer, an iPod/USB adapter, a 16-speaker premium sound system, four-zone climate control, keyless entry/ignition, extended leather trim, a rear-seat entertainment system, satellite radio and towing preparation.

The 2010 BMW X6 M is powered by a twin-turbocharged 4.4-liter V8 that pumps out 555 hp and 501 lb-ft of torque to all four wheels. A six-speed automatic with manual shift paddles is the only available transmission.

BMW claims a 0-60-mph sprint of 4.7 seconds and a maximum tow rating of 6,600 pounds when properly equipped. EPA fuel economy estimates stand at 12 mpg city/17 mpg highway and 14 mpg combined.

The 2010 X6 M comes standard with ABS (with brake assist), stability control, front seat side-impact airbags, front and rear side curtain airbags, and whiplash-reducing front head restraints.

Crash tests have not been conducted, but the structurally similar BMW X5 scored a perfect five stars in government crash tests for frontal-impact driver protection, four stars for frontal-impact passenger protection, and five stars for front and rear side protection. Also, the Insurance Institute for Highway Safety gave the X5 the highest rating of "Good" in its frontal-offset and side-impact crash tests.

The 2010 BMW X6 M has an official curb weight of 5,324 pounds. It's also a crossover SUV, so its center of gravity isn't exactly like a sports car's. So how does this beast manage to handle like a sports car? Technology. Lots of technology. There's "Active" this and "Dynamic" that in just about every area of the X6 M's operation, a battalion of high-tech aids designed to keep the laws of physics at bay. The results are stunning: Even seasoned professional drivers will be amazed at this massive BMW's neutral handling, prodigious grip and athletic character.

Thanks to an electronically adjustable active suspension, the X6 M is docile over broken pavement, too. And of course there's 555 hp under the hood, so you know you'll be faster than pretty much anything on the road. Purists will still pine for classic M cars with manual transmissions, but darned if the X6 M isn't a wholly legitimate addition to the M stable.

Take away the "M" badges sprinkled liberally throughout the X6 M's interior, as well as the special M sport seats, and you've got the same basic interior that comes with the regular X6 crossover. Fortunately, this is one of the most elegant cabins BMW has ever built. The construction is precise, the materials are high-quality and the instrumentation is crystal-clear. As expected, those M sport seats provide superb support and comfort.

The X6 M has BMW's latest iDrive interface, which includes more user-friendly physical buttons next to the control knob and a more sensible menu structure. It also has BMW's now familiar joystick-like gear selector, which drivers may find confusing due to its separate "Park" button and odd feel.