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.