And I didn’t feel the M6’s paddle-shifted sequential-manual automatic transmission harnessed the incredible 5.0-liter V10 engine with the same quick precision as the six-speed stick shift did to the 3.2-liter in-line six-cylinder of the M Coupe.

The truth, of course, was that both were memorable rides, and the M6 was faster. I got up to 130 miles per hour on a couple stretches of Road America before getting off the power and engaging the magnificent brakes to make a turn.

In the M-Coupe, I got up to 120 at two or three places on the track, but it’s lighter weight made it feel more agile and therefore more in tune with my driving instincts.

The opportunity to drive the newest BMW M models through the rolling kettle moraine countryside around the little Wisconsin town of Elkhart Lake was attraction enough, and the added opportunity to take them out on the splendid four-mile Road America road-racing circuit was irresistible.

Even though we had to hustle to finish up storming the track before Mother Nature brought in some of the blackest clouds she could muster to do a little storming of her own and curtail our dry-track fun.

The two cars we focused on were the M6, the amazingly upgraded model of the 650 Coupe, and the Z4 in M form, a dramatic upgrade on the standard Z4 Roadster and Coupe. These cars are similar in their intentions, but distinctly different in how they carry out their objective.

Insiders, and those who know what it’s like to drive various BMW models, will know exactly what the "M" means. So will BMW competitors. Mercedes has its AMG, Audi its S-Class, Ford its SVT, etc., and all of them have a good and productive time firming, stiffening, strengthening and high-powering their sportiest cars.

But throughout the auto industry, BMW stands alone. Anyone who has ever owned one will sing the praises of a 3, 5, or 7 Series BMW. Competitors would rather not talk about them, but whenever they introduce a new model, they trumpet the fact they used a BMW model as their benchmark, to prove their uncompromising attempt to achieve all-out performance precision.

When it comes to benchmarking a vehicle for its next model, BMW can only look within, at its own current models. The 330 sedan is as strong a performing sedan you can find in the compact/intermediate size; the 5-Series sedans are as hot as anyone would want in the full-size bracket.

That is, as long as they didn’t know of the availability of the "M" upgrades by those in-house hot-rodders.

BMW’s normal cars are what other companies would call high-performance. Back in 1972, BMW Motorsport began life, but it wasn’t until 1978 that the company turned the operation loose to make a one-off model, the M1 – a low, sleek, exotic, mid-engine race car. In 1984, BMW made an M6, and then an M5, both factory-prepared high-performance versions of existing coupes and sedans.

In 1986, BMW built its first M3, turning its entry-level coupe into a screamer, and later adding the "M" treatment to the four-door 3-Series sedan. In 1988, BMW sold 80,000 M3s.

Altogether, BMW has sold 110,000 M models in the U.S., which is about half the total produced. Of the rest, 30 percent go to Europe, and the remaining 20 percent are scattered around the rest of the world.

Without question, the M6 and the Z4 M models are exceptional – to say nothing of the M5 or yet-to-be-driven M3, which always has been my favorite. The technical upgrades of the M6, inside, outside, with features and that V10 engine, make it worth the $96,795 price tag for those uncompromising customers.

The Z4 M Coupe is an even bigger bargain at $49,995. Both are significantly more than their basic, non-M brethren, and if you want the pinnacle of motorized performance, you could be happy with the basic cars – as long as you don’t drive the "M" models.

For the first time, BMW has four separate "M" class vehicles for 2006, which was the reason to summon an assortment of North American auto journalists. We were picked up at the Milwaukee airport in M5 sedans.

Fantastic cars. Next morning we hopped into M6 coupes and headed off on charted drives through the countryside, and changing into M Coupes before arriving at the race track. A timed autocross was set up in the paddock, but my partner bailed out on what was supposed to be a timed run, totaling both drivers. I enlisted a BMW distribution fellow to be my partner, and I tore off around the course. The Z4 M Coupe was fantastic. It turned and swerved on cue, no leaning, no lack of precision.

At the tightest turn on the course, I floored it but the traction-control system bogged it down slightly. When it was all over, though, we finished second, giving my official co-driver reason to come out of hiding to see if we had won a prize.

On the race track itself, the M6 was a worthy ride. The car itself has been lightened with carbon-fiber and thermoplastic panels, and aluminum chassis and suspension being used to reduce weight, but it’s still 3,909 pounds.

The engine is a 5.0-liter V10, a direct descendant of BMW’s Formula 1 engine, with 500 horsepower and 383 foot-pounds of torque. The normal 650 has a 4.8-liter V8 with a mere 360 horses and 360 foot-pounds.

Skip Barber driving instructors sat in the passenger seat for all of us, and we had a good time. Two hot laps in succession, and it was over all too soon.

The M6 will go 0-60 in 4.5 seconds, with a top speed electronically governed at 155 mph. The redline is 8,250, and there is a power button you can push to hold the revs longer before each shift, and amplify the performance.

The tremendous power of the V10 sent you thundering down the straightaways, but I found the sequential automatic unsettling. Large paddles left and right on the steering wheel enact shifts of the seven-speed automatic.

The shift lever itself goes from R to N to D, then must be moved over to engage the manual phase. There is no "Park" setting, so you had to go to neutral, then pull on the hand brake.

My unsettled feeling was that I’ve driven the new Audi DSG, an incredible quick-shifting automatic that shifts faster than anyone could shift a stick. I also drove the AMG models from Mercedes, and their paddle-shift mechanism works quickly, too, if not as immediate as Audi’s. But the BMW system, which might even be more complex, took a couple of seconds – minimum – for each upshift.

I tried letting up on the gas, holding steady on the gas and stepping harder on the gas, but regardless, there was a nagging hesitation before each shift was engaged. I think one of the problems is that I recently drove the normal 650, with the six-speed stick, and found it perfect. The automatic, shifted manually, is far less fulfilling.

Countering that, the enormous, cross-drilled disc brakes were astounding. They will stop the car from 100 km. per hour (62 mph) to zero in 2.6 seconds. So, 0-60 in 4.5 seconds; 62-0 in 2.6 seconds.

There are other electronic gadgets, such as three modes of elecxtronic driver control, and two different phases of the stability control.

That’s designed to let you have a little more slippage before engaging, for those who want to hang out the rear end in performance escapades. I would need a lot more time to try out those things, but it is clear that some of these devices seem to attempt to micromanage driving instincts.

Then I got into the Z4 M Coupe. The M Coupe is the opposite, without any intrusion to offer electronic gizmos to "enhance" the driving experience. It is simple, basic, direct. I liked the Z3, and thought the Z4 was a worthy improvement, perhaps the best version of Chris Bangle’s sometimes controversial styling ideas.

The just-introduced Z4 Coupe is, in a word, an artistic masterpiece, in my opinion. I think the sloping fastback roof amplifies every contour and curve of the car.

In standard trim, the Z4 has a 3.0-liter inline six with 255 horsepower, and it will zip from 0-60 in 5.6 seconds. The "M" version takes the upgraded powertrain out of the M3 sedan and inserts it in the 3,230-pound sports car. At 3.2 liters, it delivers 330 horsepower – an increase of 75 horsepower – and 262 foot-pounds of torque. It lowers the 0-60 spurt to 4.9 seconds.

You can hit the "M" button on the console and engage a stiffer attitude with the M Coupe, but the six-speed stick and smoothly balanced engine power are a constant.

Every turn, every angle of entry or exit, every tap of the brakes, and every snick-snick gear change was as precise as a driver could make it.

Maybe that’s what I liked best about the M Coupe – it rewards you if you’re a better driver, without trying to electronically help make you a better driver.