Power is transferred to the front wheels through one of GM's butter-smooth electronically controlled four-speed automatic transmissions. They're among the best in the business.

Park Avenue also offers surprisingly good fuel efficiency, with an EPA-estimated 19 miles per gallon city, 30 mpg highway for Park Avenue and 18/27 mpg for the supercharged Ultra.

Park Avenue is built on a stiff unit-body chassis. That's a big plus, because a rigid structure ensures precise movement in the suspension. It also means that the springs, and not the body, absorb the bumps. Those two factors help suspension engineers to precisely tune ride and handling. A stiff chassis also helps reduce noise and vibration, and pays long-term benefits in durability.

Quiet operation has always been a top priority for Buick sedans, and here the Park Avenue represents a step forward. Wind noise has been reduced to a mere whisper, and the unit-body does a superior job of keeping road noise out of the cabin.

Add roomy seats with real move-around comfort, and the going becomes positively serene, particularly during freeway cruising. The Park Avenue isn't quite as quiet as a $54,000 Lexus LS 430, but the distinctions are academic in most operating situations. The distinction in price is not academic in any situation.

There is a discernible difference in handling between the basic Park Avenue and the flagship Ultra. The base model behaves very much according to stodgy Buick tradition, floating atop its wheels, with pronounced body roll and vague power steering.

We prefer not only the livelier acceleration performance but also the tighter handling of the Park Avenue Ultra. With its supercharged engine and firmer suspension, it can easily take on the best Lincoln and Chrysler have to offer. The Ultra's more positive control and firmer ride lend a contemporary feel that's a pleasant step forward for Buick.

If the Ultra's crisp handling and enhanced performance aren't important to you, then the standard Park Avenue may be the way to go. The Park Avenue comes well equipped and stacks up as an exceptional buy among large cars.

An optional Gran Touring suspension improves the responsiveness of either model. On the Ultra it costs $200 and includes unique alloy wheels and Goodyear Eagle LS Touring tires, albeit in the standard 225/60R16 size. The stiffer suspension reduces the ride height slightly and yields much sharper responses in quick maneuvers. The tradeoff in ride quality is insignificant.

On the standard Park Avenue, the Gran Touring package costs $285. That's because it includes not only the upgraded suspension, wheels, and tires but also the leather-wrapped steering wheel and Magnasteer variable-effort steering that come standard on all Ultras. Magnasteer adjusts steering effort and ratio according to vehicle speed and steering angle, keeping effort low while still providing a significantly better sense of where the front wheels are pointed. The system is even dealer-programmable for effort and feedback.

StabiliTrak stability control is standard on Ultra and optional on Park Avenue. StabiliTrak monitors yaw rate (how fast the vehicle is turning) compared to steering-wheel angle (how fast the driver wants the vehicle to turn) and selectively applies the brakes to one or more wheels to help maintain control when there is danger of sliding or skidding.

Optional Ultrasonic Rear Parking Assist can detect objects that are close behind the car, but below trunk-lid level, out of the driver's normal field of vision. Shift into reverse, and the system transmits ultrasonic beams. Four sensors in the rear bumper detect echoes, and alert the driver with a chime. The system also activates three light-emitting diodes (LEDs) set in the rear headliner, where they are visible in the rear-view mirror. Ultrasonic Rear Parking Assist works at speeds up to 3 mph; at higher speeds a flashing LED warns drivers that they're on their own. It's real handy for parallel parking as it beeps faster and faster as the rear bumper approaches the other car, allowing the driver to back the car up very close to the other vehicle without touching it.