Infiniti's Q45 looks like a thoroughbred and boasts performance to match. This is a performance luxury sedan that delivers instant throttle response and excellent handling.

As Infiniti's luxury flagship, the Q45 has to be good. It competes with the elite: Mercedes-Benz, BMW, Jaguar, Audi, Cadillac, Lexus. The people who make these cars and the people who buy them are serious about their luxury cars. Arguably, no one is fighting this battle harder than Infiniti. Infiniti has to build a top-quality performance luxury sedan, then try and sell it without the instant cachet of a brand name like Mercedes or BMW. So, like the brilliant sedans offered by those premium brands, Infiniti's Q45 is powerful, quiet, roomy and comfortable. What separates the Q45 from those other vehicles is its performance, handling and distinctive styling.

First launched 10 years ago, the Q45 has undergone refinements ever since. This year, active head restraints have been added to the front seats for improved safety. Amenities have been enhanced for more convenience and the first tune-up isn't due for 100,000 miles. The styling was revised last year.

Two models are available: Q45 and Q45t. They both come with powerful 4.1-liter V8s and firm, luxurious leather interiors.

Q45 retails for $48,895. It comes fully loaded. Among the few options available: heated front seats ($420), two-tone paint ($500), a six-disc CD changer ($718), rear spoiler ($529) and painted splash guards ($109).

Q45t comes with an electronically modulated suspension and 17-inch wheels and tires and retails for $50,595.

Infiniti's Q45 does not have the classic luxury-car appearance of a Mercedes, BMW or Lexus, nor does it have the aggressive styling of the Cadillac STS. Instead, the Q45 has an elegant look that is distinctive and stallion sleek with a long, sloping nose, a thin roof line and steeply raked rear glass. It conveys a look of luxury and performance. A strong character line separates the upper flanks from the lower and there's plenty of chrome to set it off. Five-spoke 17-inch alloy wheels give the Q45t an aggressive appearance.

Styling changes introduced last year gave the Q45 a slightly different look. The grille and the headlights were redesigned. High-intensity discharge headlights feature Xenon gas bulbs and crystalline lenses. A power glass sunroof with sunshade replaces the previous full metal type. At the rear, the combination lamps were revised.

Prestige cars traditionally offer a lap-of-luxury interior environment. The Q45 cleaves hard and fast to the traditional approach. What isn't covered in leather is covered in wood. The leather is some of the best in the business: buttery soft and perfectly stitched. It comes in three tasteful colors, beige, stone beige and black.

The front bucket seats are comfortable. The power front seats adjust in 10 directions and have power lumbar supports. Occupants sit relatively low in the car, though not uncomfortably low, providing a sense of security, a feeling of being surrounded by body structure. Visibility is good. Overall comfort is good. This car is as much at home lazing around town as it is devouring miles of Interstate. It's a nice place to be.

A two-position memory switch remembers pre-set positions for the seats and outside mirrors. An eight-speaker Bose sound system provides entertainment; and the HomeLink transmitter system opens gates and garage doors and turns on the lights in your home.

Q45 comes standard with a vast array of features that are essential in this class: power tilt/telescope steering, cruise control, speed-sensitive wipers, timed rear window defroster, dual vanity mirrors, power windows, locks, and trunk and fuel door. Separate climate controls for the rear seats help ensure passengers in back are comfortable.

The round dash-mounted analog clock is back after a two year absence and we're glad to see it. The classically styled clock was a signature item in the original Q45 and Q45 enthusiasts cried when it disappeared.

The Q45 comes with dual front airbags and side air bags that deploy from the front seats and front seat belt pre-tensioners. There are pick-resistant door locks. If, somehow, the castle has been breached, the perpetrator will run up against the Infiniti Personalized Protection System that combines 60,000 possible key codes with a new, numerically random rolling code generated by the engine's computer each time the ignition is turned off.

Among the few options available is the Infiniti Communicator ($1599), which includes a cellular telephone and Global Positioning Satellite system. Two buttons in the overhead console contact the Infiniti Response Center, which will contact emergency road service or medical help. If the air bags deploy, the center is automatically notified.

A nice touch we liked is the Interior Light Logic feature. It turns the interior lights on very brightly in the open door for easy entry and exit without blasting the rest of the cabin with intense light. We also liked the pin light that bathes the center console and front door panels with soft light that makes finding and operating controls a bit easier.

The Q45 performs like a thoroughbred. Infiniti's 4.1-liter engine gives the Q45 stellar performance. Based on the same powerplant as the Infiniti Indy V8 used in the Indy Racing League cars, it generates 266 horsepower and 278 foot-pounds of torque. It features variable valve timing, which adjusts valve opening and closing according to engine speed and load. Variable valve timing is a key element in the engine's efficiency and is a proven technology.

Performance has always been an Infiniti trait and there's lots of power here. Although peak torque is at a relatively high 4000 rpm, there is usable torque low in the power range and that means great acceleration at lower speeds. Throttle response is instant, whether you're moving away from a stoplight, making a tight freeway merge or passing. The Q45 accelerates from 0-60 mph in the mid 7-second range. That's quick. It also delivers responsible fuel economy, netting an EPA rating of 17 mpg city/24 mpg highway.

This V8 is among the smoothest and most satisfying around today, easily holding its own with Lexus and BMW offerings and perhaps even a touch smoother and quieter than the Mercedes-Benz V8s. The Q45 has always been more of a driver's car than the Lexus LS 400 and that tradition continues. The V8 drives the rear wheels through a four-speed electronically controlled automatic transmission; smooth, precise shifts are based on speed and load. On the road, the feeling is of a seamless flow of power with no hesitation or jerkiness between shifts. A viscous limited-slip differential with traction control reduces wheelspin in slippery conditions.

The MacPherson strut front suspension was designed to provide good handling without compromising on that luxury car feel. In the rear, the Q45 has a multi-link arrangement designed to keep more tire contact patch on the road, and more patch means more grip. Anti-dive and anti-squat characteristics mean improved grip under hard braking and acceleration.

The Q45t (Touring Package) has a slightly more aggressive suspension tune for a sportier feel. Still, the ride quality is excellent.

This car always feels firmly planted. It's stable as a freight train in a straight line, controlled in turns. The Q45 feels very nimble for a large luxury car. Steering is razor sharp, quick and precise. The suspension is well damped, isolating occupants from poorly maintained road surfaces. But it doesn't float like some big luxury cars that use mushy suspensions to make up for poor chassis engineering. You won't have any trouble keeping up with BMWs in a Q.

The Infiniti Q45 offers excellent performance and handling. It's a real driver's car. Yet it also delivers a well-damped ride, a comfortable driver's interior and a luxurious traveling experience. It can hold its own against the best world's luxury cars.