Unification is a wonderful thing. In terms of Infiniti's G37, it applies not only to the union of coupe, sedan and convertible models but also to the line's harmonious blending of performance and luxury. Last year's coupe became the first to wear the G37 badge, owing to its larger and more powerful 3.7-liter V6 engine; the sedan model, however, retained the G35 name, in keeping with its carry-over 3.5-liter V6. Now, with the 2009 sedan also gaining the larger engine and a convertible joining the stable, the lineup is unified under the G37 banner.Thanks to the ideal weight distribution provided by Nissan's second-generation FM platform, not to mention that brawny V6 power plant, the 2009 Infiniti G37 has performance entrenched in its bloodlines. But the G37 is about far more than just going fast -- it also boasts an attractive cabin, a plethora of high-tech features and a suspension that's supple enough for the daily commute. The G37 is further enhanced this year by a new seven-speed automatic transmission, which promises slightly better fuel economy and acceleration than last year's five-speed.In a nod to modern trends, the new G37 convertible has a retractable hardtop that flips, folds and stows beneath the trunk lid in less than 30 seconds. Infiniti prides itself on having to add just a quarter-inch to the overall length of the G37 coupe in order to create the convertible. Several convertible-specific features are offered, including standard pop-up roll bars and the Bose Open Air sound system with headrest-mounted speakers. Increased structural bracing reduces body shimmies to just an occasional subtle waggle in the lower cabin when traversing pavement buckles, but the convertible ends up weighing about 450 pounds more than the coupe.Infiniti's G series was already one of our favorites, and its standing rises even higher considering its improvements for 2009. As usual, however, there are a plethora of great choices in the entry-level luxury segment. BMW's 3 Series, which has also been updated for 2009, remains the gold standard in this class, though the G37 handily outperforms the 328i for about the same price. Other models, such as the Audi A4/A5, Cadillac CTS and Mercedes-Benz C-Class, have their own particular strengths and are well worth taking for a spin. But the G37 is definitely deserving of your consideration. Its unification of performance, comfort and style is a wonderful thing indeed.