The dynamic portion of our test drive took place at the Road Atlanta raceway. Slinging this beast around those high-speed bends, I quickly gave up on full manual gear selection. As with most modern "smart" trannies, the automatic's sporting S mode gives an almost clairvoyant insight into your driving mindset; in this case, it facilitates maximum performance while allowing more concentration on following your line than on flailing for gear levers or slapping at aluminum paddles cranked at unaccommodating angles.

Power goes to the ground through BMW's proprietary four-wheel xDrive system. In this case, xDrive uses what they call optimum dynamics; essentially, it's been set up for a greater power bias toward the rear. But the variable power distribution remains programmed to read driving conditions and direct power fore or aft, even before wheels start to slip, in order to preclude both under- and oversteer and pre-empt stability control interference.

With such prodigious levels of power, mass, and grip, it's frightening to imagine things going horribly out of shape. An out-of-control X6 M would seem to constitute an astounding release of energy, something on the order of splitting atoms. That's where you come to appreciate the inherent safety and driver-aid systems: DSC stability electronics, the M-tuned air suspension, Adaptive Drive with electronically adjustable dampers (EDC), and active anti-roll.

And in case you like to tempt fate, M Dynamic Mode (activated by the DSC button) raises the intervention thresholds of the aforementioned systems. Your inner hoodlum will likely approve.

Did the world need a 550-hp SUV, much less two of them? Probably not, but the idea remains a compelling one. And in spite of this apocalyptic age, these are two of the most powerful yet. Priced just south of $90,000, they look to be wholly competitive in the ML63/Cayenne Turbo landscape. Whether or not the market will continue to embrace such vehicles is another question. But in terms of sheer audacity, each must receive our seal of approval.

2010 BMW X6 M
Longitudinal front engine, all-wheel drive

4.2-liter V8, dohc, 32-valve, turbocharged and intercooled

Six-speed automatic

Double-wishbone/multi-link front, Integral IV (four-link) rear, BMW M-specific elastokinematics and springs

Four-piston fixed calipers, 15.6-inch rotors (f), single-piston floating calipers, 15.2-inch rotors (r)

Length/Width/Height (in.): 192.0/78.1/66.3
Wheelbase: 115.5 in.
Curb Weight: 5,326 lb

Peak Power: 547 hp @ 6000 rpm
Peak Torque: 500 lb-ft @ 1500 rpm
0-60 mph: 4.5 sec.
Top Speed: 155 mph (limited)

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