It's easy to get bogged down in superlatives with such a car -- not that there really are any other cars quite like this -- so let's begin our dialogue with the numbers.

The BMW M5 sedan can accelerate to 60 miles per hour in less than five seconds. It can accelerate to 100 m.p.h. in just over 11 seconds, cover a quarter-mile in less than 13.5 seconds and reach 150 m.p.h. in 30 seconds. Such numbers wouldn't raise eyebrows if they were generated by a Corvette, but the M5 obviously is not a Corvette.

It's a leather-lined, four-door luxury sedan crammed with high-tech goodies. It weighs in at about two tons -- not exactly the kind of mass you'd associate with those blistering performance statistics.

It's not the kind of mass you'd associate with agility worthy of a cheetah, either, but that's exactly what this sizzling sedan delivers. Even among the many offerings of a company known for cat-agile automobiles, the M5 stands out as something special.

I suppose you could object that its ability to change directions might not be quite as instantaneous as a Corvette or Porsche 911, but you'd need specialized test gear to quantify the difference.

More significant, in the realm of luxury sport sedans, the M5's immediacy of response is pretty much in a class by itself. The Jaguar XJR and Mercedes-Benz E55, which are also seriously potent factory hot rods, are the only other four doors that come close, but the M5's performance is tops nevertheless.

That also applies to its braking prowess. All three of these super sedans are armed with oversize brake rotors and sophisticated antilock systems, but the M5's brakes take the cake, albeit by a small margin.

And best of all, from a stealth point of view, the M5 doesn't look vastly different from its less-potent counterparts in BMW's 5-Series collection, the 528i and the 540i.

The 18-inch wheels have a different design and wear low-profile performance tires. The front end has a different look, thanks to a slightly deeper air dam, the rocker panel extensions along the sides are just a bit more pronounced, and there's a tiny little spoiler, not much more than a half-inch high, on the rear decklid.

Motorsports models

Beyond that, only the telltale M emblem betrays the car's expanded capabilities. M stands for motorsports in the BMW lexicon, and in the last five years or so BMW cars wearing that badge have accounted for a steadily increasing percentage of the company's annual sales.

In fact, there are M versions of just about everything in the BMW lineup, a distinction that will even apply to the new X5 sport-utility family. The M models are developed through a separate corporate motorsports hot-rod shop, and the treatment includes enhancements to the engine, suspension, brakes, wheels, tires, and relatively minor cosmetic tweaks.

This special marketing program has been so successful that it's inspired competitors to do likewise .

Mercedes-Benz, for example, has been offering an increasing number of heated-up versions of its cars, as well as the ML-Class sport-utility. The conversions are carried out by AMG, once an independent performance tuning specialist that's been taken in-house by Mercedes.

And I have a feeling we might see something similar from Jaguar.

Considering what the M5 can do on a racetrack, this car also delivers astonishingly good ride quality. Do you sense a proviso here? Yes, you do.

Getting a car to maintain flat cornering attitudes and near-neutral handling balance means stiffening the suspension components, which in turn inevitably means compromising the ride.

That's the case with the M5, which is a little less supple over sharp bumps and other pavement irregularities than the more mainstream members of the 5-Series lineup -- but not by much.

I suppose folks who like the sofa cushion isolation of, say, a basic Lincoln Town Car, might characterize he M5 as stiff, but I think that anyone who appreciates the sense of sports-car control that goes with such a thoroughbred as this would be more than pleased -- amazed -- at its comfort.

Amazing comfort

The biggest functional distinction inside the M5 vs. the standard 5-Series sedans is a set of extra-supportive adjustable power bucket seats up front. They're leather, of course, and like most BMW buckets they're reminiscent of racing seats, with deep thigh and torso bolsters to keep driver and front seat passenger from sliding around during vigorous cornering. They do an excellent job of this and also provide exemplary long-haul comfort.

My only objection is the two-tone Sport color scheme, something BMW offers in its other M cars. In this case, the colors were black and red, to echo the tomato red exterior -- a little garish for my taste.

Another Sport decor element that just doesn't work is the titanium-hued trim panels installed where you'd find wood on other luxury cars. It looks distinctly tacky in this car. So does the similar plastic covering on the shift knob. If I were ordering, I'd go for the more traditional Exclusive interior package, which is all black with wood trim.

Not a roomy M5

Aside from limited rear seating capacity -- as with so many cars in this size class, the 5-Series sedans are rated as five-passenger conveyances, but four is really the comfort max -- the M5's interior is otherwise exemplary.

Standard equipment includes an excellent navigation system that incorporates an audible direction feature. Program your destination into the system, and a woman's voice tells you when and where to turn. It seems to be generally quite accurate, and the only thing that would make it better is if the voice sounded like Marlene Dietrich.

Another noteworthy feature is BMW's new side air bag that deploys along the roofline to provide head protection in side impacts -- this in addition to side air bags for thorax protection.

And, as you'd expect at this price level, there's a lengthy list of power-operated luxury features, including automatic climate control and a superb sound system. Oh, yeah, don't forget the ultrasuede headliner.

Still, the element that truly sets this car apart is its power train. Based on BMW's excellent 4.4-liter aluminum V8, the M5's 4.9-liter version, which is chock-a-block with high-tech power enhancements, generates 400 horsepower. That's a serious herd of ponies, more than any other regular production sedan, in fact, and also more than all but a few super sports cars.

This sweet-sounding power generator is bolted to a six-speed manual transmission -- the only transmission offered with this car -- that's a model of precision and an absolute pleasure to employ.

It's hard to imagine anyone who loves to drive becoming tired of operating this fabulous system. But it's clear that this amazing automobile isn't for everyone. At $73,874, including destination charges, guzzler penalties and luxury tax, it's beyond my means and maybe yours, too.

But if it's not beyond your means, and a super sedan has been on your wish list, do not deprive yourself of the opportunity to drive an M5.

Just one warning: Once you drive this car, the odds are you'll never be satisfied with anything less.

SPECS
Rating: 4 Stars

Vehicle type: Front-engine, rear-drive luxury sedan

Key competitors: Jaguar XJR, Mercedes-Benz E55

Base price: $73,874

As tested: $73,874

Standard equipment: ABS, Dynamic Stability Control, dual threshold front air bags, side air bags, CD/GPS navigation, power sunroof, automatic climate control, AM-FM-cassette audio, heated power leather seats with memory presets, trip computer, power windows with one-touch up and down, keyless remote entry, heated power mirrors, power locks, power tilt-telescope steering, cruise control,a uminum alloy wheels

Specifications

(Manufacturer's data)

Engine 400-horsepower, 4.9-liter V8

EPA fuel econ. 13 m.p.g. city, 21 hwy.

Curb weight 4,050 pounds

Wheelbase 111.4 inches

Length 188.4 inches

Width 70.9 inches

Height 56.7 inchesWhere assembled Germany