The CLS is roughly the same size as the E-Class sedan, with which it shares a number of major components.Yet the CLS-Class features fewer variants than the E-Class and it occupies a higher range on the price scale, with more standard luxury equipment.What distinguishes the CLS most readily from other Mercedes sedans is its four-seat cabin and gorgeous exterior styling.It comes in two varieties: Powerful and crazy powerful.

The Mercedes-Benz CLS550 is powered by a 5.5-liter V8 that develops 382 horsepower and 391 pound-feet of torque.If that isn't enough for you, the Mercedes CLS63 AMG features a 6.2-liter V8 rated at 507 horsepower and 465 pound-feet of torque.Both engines are matched to a seven-speed transmission.

But it's styling that distinguishes the CLS.Technically, the CLS is a sedan because it has four doors, but Mercedes calls it a four-door coupe, and that's a good description.The swoop-roof, pillar-less CLS has the graceful, sensuous, feel of a coupe with the rear-seat access of a sedan.It may be the most visually appealing four-door on the market.Those great looks come with a slight penalty in terms of interior space, of course.The CLS only has four seats with four seat belts, while the E-Class cars have five.

In terms of technology, however, the CLS gives up nothing.Its air-spring suspension automatically gets firmer or softer depending upon road conditions.A vast array of Mercedes safety features come standard, including rear-passenger side-impact airbags and one of the most advanced skid-management systems in production.More than 70 percent of the steel in the body and frame is galvanized, high-strength alloy, and even the paint is advanced.The clearcoat layer is impregnated with tiny ceramic particles, increasing resistance to scratches by 300 percent compared to conventional finishes, according to Mercedes.

For 2009, CLS gets minor changes to its exterior appearance.The four-bar grille is replaced with a two-bar version, the mirrors are larger and include built-in arrow-shaped turn signals, and there are new dual-five-spoke 18-inch wheels.In back, there's a new rear bumper with trapezoidal-shaped dual exhaust outlets and arrow-shaped LED taillights.Inside is found a three-spoke steering wheel with a sportier appearance, new gauges in white with silver backgrounds, and a revised central display in the console incorporates Bluetooth for hands-free phone operation, a six-CD stacker and voice control of audio and phone functions.

Options include the Premium 1 Package ($3,950) with active ventilated front seats with heating, power rear-window sunshade, bi-xenon active light system, KEYLESS GO, iPod/MP3 media interface, headlamp washers, and electronic trunk closer; the Trim Package ($920) that includes a wood and leather shift knob; and the Sport Package ($5,090) with steering wheel gearshift paddles, 18-inch AMG wheels, Sport Bodystyling, and sport tires.Stand-alone options include Distronic radar-guided cruise control ($2,230), Parktronic park-assist warning ($1,140), and illuminated doorsills ($875).

The Mercedes-Benz CLS63 AMG ($96,300) comes with an air suspension tuned for sharper response and flatter cornering, larger Z-rated tires, and more powerful brakes.Its seven-speed automatic features Speedshift paddle shifters that allow it to work like a manual transmission without the clutch pedal.

Safety features that come on all CLS models include front multi-stage airbags, side-impact airbags for front and rear passengers, front and rear curtain-style head protection airbags, seatbelts with pre-tensioners and force limiters, ABS with Brake Assist, Electronic Stability Program, a roll-over sensor, low-tire warning system and Tele-Aid emergency telematics.

The sedan quality derives from one obvious characteristic.It has four large, conventionally hinged side doors that allow unfettered access to both the front and rear seats.

Its coupe qualities are harder to define, but it's that makes the CLS so interesting and attractive.And it's not just its long, low-slung profile.It's the frameless side windows, the barely-visible center roof pillar, and the descending slope of the rear pillar, which blends into muscled rear fenders.A pronounced shoulder line sweeps back from the front wheel arch, creating a wide, tall-waisted stance, as though the car has been stretched by the wind.It's hard to believe that a tilt/sliding glass sunroof will fit within the arching roofline, but it does.

The front of the car thrusts visually forward with prominent grille slats, a deeply wedged hood and fenders that dive steeply into the distinctive headlamp clusters.A deep bumper forms a coupe's characteristically muscular rear, braced by two chromed exhaust pipes.

The CLS features details that reduce noise when cruising at high speed.Look closely and you'll discover things like plastic deflectors in front of the front wheel arches to improve airflow across the front axle links, aerodynamic cladding on the rear axle spring links, and mini-spoilers in front of each wheel to reduce dynamic pressures at the tires and improve airflow around the wheels.Even the wiper arms were refined in the wind tunnel.These aerodynamic wipers feature a mounting system and integrated spoiler for better wiping with less noise.

We're not sure we love the looks of the aggressive lower body cladding on the CLS63 AMG.It's just not as pretty as the CLS550.The staggered-width, 19-inch five-spoke AMG wheels look fantastic.The deep front and rear aprons and sculpted doors sills are anything but ugly, yet they take away of the graceful shape.That's sometimes the case with racy versions of beautiful cars.

The CLS cuts a fairly slippery profile, with a drag coefficient of 0.31, low for such a sculpted four-door car.This aerodynamic efficiency contributes to overall fuel efficiency and reduces wind noise at high speeds.The AMG rides a half-inch lower than the standard CLS.

The view forward is filled by an expanse of burr walnut that stretches between round vents in the far corners of the dash, finished in a silk matt rather than the high-gloss familiar in many Mercedes.The walnut surface is broken by recessed center air vents, the climate control switch cluster and the main instrument cluster, which features three chronometer-style gauges and two LCD bar graphs for fuel level and coolant temperature.Each gauge is ringed with chrome, as is the cluster as whole.The graphics are crisp, and covered with a special mineral glass that virtually eliminates glare.

Fit and finish is terrific, and the custom-tailored feel is enhanced by the design.Note how the front passenger airbag door blends perfectly into the upward sweep of the walnut panel.Note how the chrome-and-walnut theme carries down through the center console, with a ring surrounding the transmission shift lever, and into the rear cabin, with a separate walnut panel and chrome trim for the rear-seat climate controls.Note how the curve of the center rear console is reflected in the reverse curve of the outboard armrest.

All four seats are covered in leather, with a thicker, richer Nappa finish in the CLS63 AMG.The standard front seats are adjustable 10 ways, using Mercedes' patented seat-shaped switches.There are three memory storage settings, and they can be matched to the remote key fob.Most switches are conveniently placed.A color display screen incorporates audio controls, navigation system and most other functions into a single set of switches.It takes time to learn, but I prefer it to the point-and-click devices in many luxury cars.

The standard harman/kardon Logic 7 stereo sends 480 watts of audio through 12 speakers.Digital processing allows the driver to tailor sound to his or her taste, or to create a surround effect for any seating position.

In the rear seats, the sexy exterior styling results in a decrease in headroom, compared to a Mercedes E-Class.As part of our familiarization with the CLS, we were chauffeured across Rome so that we might see how the rich and famous do it.Tough job.My six-foot frame was comfortable on winding city streets, but passengers much taller may step out of the CLS with a crick in the neck.

Trunk space is not a problem, however.With 15.9 cubic feet of volume, the CLS trunk offers exactly the same space as the E-Class sedan, and not much less than the larger S-Class sedan.

In terms of interior comfort, the CLS makes for a great four-passenger sedan.

The CLS63 AMG goes almost like a race car and stops like a sports car.Its 6.2-liter V8 is not only blindingly quick, it's also super smooth.And it also has a racing-style dry-sump lubrication (a separate oil tank instead of the traditional oil pan at the bottom of the engine), which ensures proper oiling under extreme g-forces.

The seven-speed automatic transmission pairs with the 6.2-liter V8 to form a very impressive powertrain combination.Throttle response is instantaneous, automatic downshifts nearly so.The manual control electronics, which allow a driver to shift the transmission like a manual using either the shift lever or paddles on the steering wheel, are excellent.It allows the driver to hold a gear right at the engine's redline, where it's still silky smooth.Finally, there's a nice burbly exhaust tone at part throttle, with something more like a rebel yell when you floor it.

In the CLS63, the air suspension is tuned with a bias toward the handling side of the equation, or more firmly than some owners might like.It's also fitted with larger, Z-rated tires.In our view, it's not uncomfortable, and the payoff in improved response is worth it.Most Mercedes-Benz cars will go along for the ride when pushed, behaving predictably.The CLS63 AMG likes to be pushed.Think of it as a more willing participant in a spirited drive.

NewCarTestDrive.com correspondent Greg Brown filed this report from Rome.