KOHLER, WI – BMW AG’s now-famous Motorsports Div. – usually just “M” for short – is the in-house tuner unit that for decades has been emulated by auto makers the world over.

Oddly, though, in these times of rampant model proliferation, the company seldom has more than a couple of M models in production in the same model year.

Meanwhile, there’s an onslaught of copycats from chief rivals Mercedes-Benz AG, Audi AG, General Motors Corp.’s Cadillac Div. – not to mention downmarket alternatives from Ford Motor Co. and Chrysler Group.

By the end of the year, Mercedes will be selling 14 models modified by its AMG division.

BMW has had enough. It’s answering with two new M models – the Z4 M Coupe and the M6 – doubling its stateside M arsenal and adding another two, the M3 and M6 convertible, this fall.

In 1984, the 6-Series was the donor platform for the 635CSi, the first M car based on an existing BMW production car. So it’s appropriate the new ’06 M6 becomes the flagship of the M division’s lineup.

And what a flagship. From the storming 500-hp 5L DOHC V-10 to the controversial SMG automated-manual gearbox to its host of high-tech materials applications, the M6 is one of those cars in which the sum of its parts actually exceeds its imposing road presence.

And make no mistake, the M6 has road presence. Photos don’t do justice to how richly the car hunkers over its excruciatingly beefy fender flares and 19-in. alloys, the minimalist greenhouse squashed onto the curving sheet metal like something out of a Hot Wheels catalog for rich kids.

And the kicked-up trunk kink that so startled the world when BMW design guru Chris Bangle unleashed it for the 7-Series works brilliantly here, adding visual heft and reinforcing the M6’s connection with the rest of the BMW cosmos.

Eye the M6 from any angle and the sheet metal leaves no doubt this is an expensive car.

Sometimes, there’s no sheet metal. The M6’s roof panel is fabricated from carbon-fiber reinforced plastic (CFP), which engineers say shaved 9.9 lbs. (4.5 kg), not to mention enabling a lighter rear window. The CFP is used for front and rear bumper supports, as well.

The doors and hood are aluminum, the front fenders thermoplastic, the rear decklid, sheet molded composite.

And like many BMW production cars, most of the platform’s front structure is aluminum, as are significant portions of the front strut and rear multilink suspensions.

BMW says the curb weight of 3,771 lbs. (1,710 kg) is 99 lbs. (45 kg) lighter than the 4-door M5, something of an accomplishment because traditionally, these technology- and feature-laden premium coupes have not been renowned as featherweights.

Shaving weight helps handling and acceleration, and the M6 dishes out both qualities with aplomb.

The all-aluminum 5L DOHC V-10, first used in the M5, surely is one of the world’s most impressive series-production engines.

For the M6, it seems BMW engineers may have slightly cocooned the passenger compartment from the priceless yowl of the V-10 when its 10 individual throttle butterflies are cracked wide open (electronic actuators do so in just 120 milliseconds).

But nothing can save you from your giddiness when the sometimes cantankerous SMG falls in step and all 500 horses hook up to spit the M6 down the road like a fireball from a Roman candle.

There’s enough technology just in the remarkable V-10 to justify the M6’s stiff $96,795 base price.

But not to be missed are features such as the “power” button that, when depressed, summons all 500 hp – in typical driving, the engine-management system defaults to a less socially deviant 400 hp – and makes the throttle and other engine-control features more hyper-active.

Inside the M6, there’s all the coddling someone dishing out six figures expects. The seats are sumptuous and grippy, and all the interior materials are excellent and meticulously applied.

The Siemens VDO Automotive-designed color head-up display is a particular treat, showing the gear position of the 7-speed SMG (helpful in that the transmission confounds in so many ways) surrounded by a digitally generated ring to simulate the tachometer.

The 3-spoke steering wheel seems a bit plasticky, and the dreaded i-Drive control knob is intelligently offset to the right of the center console, the better to employ the exquisitely detailed gearshift lever.

If the M6 is all about sublime performance, the other M-car BMW shows to the media here, the Z4 M Coupe, is its diametric opposite.

First, forget the subtle fluidity of the M6’s lines. The Z4 M Coupe is an amalgam of intersecting curves and surface details, as abrupt (jarring, some would say) as the M6 is creamy and smooth.

The defiantly taut shape seems to be an acquired taste. Many see shades of BMW and other European coupes of an earlier generation; others find no joy in so much design “busyness” in so small a package.

Likewise, the M Coupe’s performance is a contrast to the measured explosiveness of the M6.For the M Coupe, just leave off “measured.”

The 3.2L DOHC I-6 that long has powered the M3 coupe is pressed under the long hood of the M Coupe, just as it is for the Z4 M Roadster. Few situations demand a driver’s attention as resolutely as unleashing this engine’s 333 hp on 3,230 lbs. (1,466 kg) of short-wheelbase coupe.

Crack! One’s head snaps on the first gear-second gear shift, the rear wiggles under the strain of too much power and the steering wheel writhes as the Z4 M Coupe – it’s chief reason for being, apparently, to compete with the coincidentally just-launched Porsche Cayman – bolts from 0-60 mph (97 km/h) in less than five seconds.

“Stupid fast” is too serene a term for the Z4 M Coupe.

At least the spectacular brakes, borrowed from the special-purpose M3 CSL, are on duty to bring sanity to the proceedings. And on back-road test drives here, we’re happy for the security of Dynamic Stability Control, and would not consider even partially disarming it, as is possible with the M6.

A former colleague, not impressed with Nissan’s 350Z, once called it a “Japanese Trans Am.” One is tempted to call the Z4 M Coupe a “German Trans Am,” as refinement is not a strong suit, particularly when accounting for the notchy reluctance of the ZF Friedrichshafen AG-made 6-speed manual that is standard or the general sturm and drang of the interior.

Crimping a roof onto the Z4 roadster may have added a healthy dose of structural rigidity but did nothing for the noise, vibration and harshness attenuation in the already constricted interior. As thrilling as the Z4 M Coupe’s performance is, we couldn’t advocate its merits for interstate cruising.

However, if one’s appreciation for European-style panache trumps the need for creature refinement, the Z4 M coupe, at $49,995, delivers thrill-ride acceleration and top speed (if you dare) wrapped in attention-grabbing sheet metal that also happens to wear the BMW propeller badge. Uniqueness is assured.

BMW engineers couldn’t engineer a solution to avoid the Z4 M Coupe’s $1,000 gas-guzzler surcharge. The $3,000 guzzler tax slapped on the M6 is at least understandable for a big-dollar, big-engined GT car but seems unnecessary, regardless of how much engine it has, in a 161-inch (409-cm) compact coupe.

It probably guarantees neither the Z4 M Coupe nor the M6 will be on Al Gore’s ’06 shopping list.