Purists have decried that "X" and "M" sharing a bootlid is the death of the brand, but these newest additions are just the latest in a long string of M-badged expansions. The brand's original intent – producing homologation specials tailored to die-hard enthusiasts – underwent its first conniption-inducing phase when BMW introduced the E30 M3 Convertible. Devotees cried foul, but amazingly, the brand not only survived, it thrived. Similar (if less vocal) protests were heard when the six-equipped E36 model debuted, followed by the E46 and the latest V8-powered model.



While that broken record is wearing thin, there's no doubt that the M brand is completely unrecognizable two decades later. It's moved beyond motorsport to bring power, agility and engagement to the masses through BMW's bread-and-butter models. And in the case of its fire-breathing SUVs (errr... SAVs), it's a story we've seen played out by another German automaker and its controversial introduction of a high-performance 'ute. We know how well that turned out, and now we know this: the X6 M has the goods to dominate its aging competition from Stuttgart – even if BMW doesn't want us to draw comparisons.

Packing a reworked version of the 4.4-liter twin-turbocharged V8 initially fitted to the X6 xDrive50i and later on the 2009 7 Series, the S63B44 has been tuned to deliver 555 hp at 6,000 rpm (five horsepower more than the Cayenne Turbo S – oops, we did it again) and 501 lb-ft of twist from an oh-so-low 1,500 rpm all the way through to 5,650 rpm. The party ends at 7,000 RPM, but outputs only tell a fraction of the tale.



An ingenious (and patented) exhaust manifold lies between the engine's two cylinder banks, shuttling spent hydrocarbons through four individual exhaust runners, then two tuned tubes feeding a duo of twin-scroll turbos. With a compression ratio of 9.3:1, peak boost of 7.3 psi and precise pulses of exhaust gas keeping the turbos perpetually on boil, the X6 M nearly eliminates any hint of turbo lag and sets a new bar for force-fed throttle response.

BMW claims a 0 to 60 mph run of 4.5 seconds (without launch control) and we have little doubt it's more than capable of shaving a tenth or two from that figure depending on the testing method. But straight-line performance aside, this V8 is among the quickest, most linear turbocharged engines we've ever tested and the transmission delivers shifts nearly on par with the world's best dual-clutch gearboxes.

The six-speed auto 'box is a mildly reworked variant of the ZF unit found on the standard X6, and in either automatic or manual modes, the tweaked six-speed has found a soul-mate with the twin-turbo'd V8. The amount of programming that's gone into delivering seamless shifts boggles the mind, specifically the ECU's ability – in Sport mode – to cut ignition to one cylinder while locking the torque converter to deliver a completely imperceptible suspension of torque.



Although the shifts aren't nearly as impressive when the awkward but adaptable transmission stalk is set to Auto, the steering wheel-mounted paddles are laid out as God intended – upshift on the right and downshift on the left – and they are easily snatched for passing power on demand. To lay into the throttle in Auto mode is to take a beat and feel your kidneys wrap around your spine as all four wheels grapple the tarmac and a muted, aggressive howl erupts from the quad-tipped exhaust.

While the transmission is excellent and the engine is beyond reproach, the all-wheel drive system and its assorted acronyms prove BMW has signed a pact with the Devil – one that cuts both ways and doesn't include a trip to Jenny Craig.

Originally fitted to the X6, the AWD system features BMW's torque-vectoring Dynamic Performance Control (DPC) which shuffles power between the rear wheels to maintain a constant cornering attitude no matter the conditions. It's unobtrusive and highly adaptable, accelerating the inside rear wheel when it detects oversteer, delivering more grunt to the outside rear wheel to keep understeer at bay, or sending the majority of the power to the rear wheels when nailing the long pedal in a straight line. Navigate to the vehicle settings page in the (much improved) iDrive system and passengers can see exactly which wheels are getting precisely measured delivery of torque. But it's best to avoid the desire to stare at the display, as the next corner presents itself a quickness... and you've got an unwieldy amount of mass to manhandle into submission.



When the time comes to turn, the X6 M's natural tendency is towards understeer. Set to Sport, the Electronic Damping Control (EDC) and Active Roll Stabilization (ARS) do their best to mitigate the effects under load, and with a double-wishbone front and multi-link rear suspension dropped by half-an-inch and fitted with stiffer bushings, body roll is all but eliminated.

Hit the "M" button on the steering wheel, and with M Dynamic Mode (MDM) engaged, the ghosts in the machine allow for a limited amount of rear slip. Defeat the traction control completely – as we did after a hot-lap with the head of BMW's suspension development – and the X6 M's attitude changes ever-so-slightly, allowing for greater slip angles that won't set the fastest laps, but leave you cackling like a demented five-year-old with a gross of firecrackers.

Despite the electrowizardry adding an extra layer of anesthetic to the experience, there's a twisted appeal to be had in piloting a high-riding crossover with an elevated seating position at triple-digits speeds, only to chuck it into a 90-degree left-hander. In a weird, physics-defying way, all was right in the world – until our fourth lap around Road Atlanta.

Heading downhill towards Turn Six, with the weight of the world (and yes, you've been waiting patiently for it, 5,324 pounds) on our shoulders, we laid into the stoppers. The pedal traveled halfway towards the floor before the X6 M began to slow. With less than 100 feet before our turn-in point, we eased off the brakes, then reapplied and forward progress was mercifully interrupted before we had the chance to test the SUV's heightened ride on an impromptu farming excursion. Turn Seven came up just as fast and the process had to be repeated. And again. And again. With its uprated 15.6-inch discs clamped by fixed, four-piston calipers in front and 15.2-inch rotors with single-piston calipers in the rear, the X6 M has the stopping power on paper to put up with this porky, high-output SUV. In torturous practice, less so. While we're not convinced the X6 M will be seeing regular track duty (particularly on a course as demanding as Road Atlanta), this is an "M" after all, and fade isn't the order du jour. We're looking forward to a full review to see if the problem persists, but somehow, we doubt it will.



Although the real M-ification of the X6 lies underneath its sheetmetal, there's little to discern the standard four-door coupe/SUV/SAV from its lesser brethren. It gets the standard gaping front grilles and fender vents, along with body-colored rocker panels and M-specific 20-inch rolling stock (fitted with 275/40 R20 front and 315/35 R20 rear run-flats) that almost appear too small in the massive body-matched wheel arches. But the overall effect is subdued, or at least as subtle as the this massive hatchback on stilts could reasonably attempt to be. It's no sleeper and it wasn't designed as such, and BMW takes pride to point out that X6 M owners are, "self-confident extroverts." No doubt...

For M addicts looking for more juice from their Roundel-badged SAVs, the X6 M is the only game in town, and at $89,725, it's likely to quell cross-shopping as it undercuts the Porsche Cayenne Turbo by a considerable margin. Add the X5 M into the equation and you've got an added dose of practicality with less divisive looks. No matter the body style, you'll be piloting one of the most formidable, meticulously engineered, tech-rich crossovers on the planet, perfected for those corrupted by power and enamored by grip – and it's likely the last of its breed.



Undoubtedly, the world's Chicken Littles will shudder at the idea of a 555-hp crossover, but the underlying technology -- forced induction, all-wheel drive and copious quantities of electronics -- that makes the X6 M such a perspective-skewing vehicle will eventually find its way into the next generation of BMWs and M products. Lightweight, fuel efficient, turbocharged offerings are right around the corner, packing enough performance to rival their modern-day counterparts while treading slightly lighter in the process. If that's the future, the X6 M is an unlikely harbinger. But we're ready for it. M is dead, long live M.



Photos Copyright ©2009 Damon Lavrinc / Weblogs, Inc.