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.

The 2009 Infiniti G37 is an entry-level luxury sport coupe, sedan or retractable-hardtop convertible offered in four trim levels -- base, Journey, G37x and Sport 6MT -- except for the convertible, which is offered only in base or Sport 6MT trim. The base G37 comes standard with 17-inch alloy wheels (18s on the coupe), xenon headlights, keyless ignition and entry, automatic climate control, leather upholstery, full power accessories, power front seats, a tilt-and-telescoping steering wheel and a six-speaker audio system with a CD/MP3 player, satellite radio and an auxiliary audio jack.

The Journey trim level adds automatic headlights, dual-zone climate control, a six-CD changer and added passenger-seat power adjustments. Stepping up to the G37x all-wheel-drive model adds heated front seats and outside mirrors. The Sport 6MT trim level brings added performance features and the six-speed manual transmission. It comes standard with 18-inch wheels with high-performance tires (19-inch wheels on the coupe), sportier exterior and interior treatments, a limited-slip rear differential, upgraded brakes, a sport-tuned suspension and seats with added thigh and torso support.

There are no options available for the base G37. Options for the Journey, G37x and Sport 6MT trim levels are numerous but are available largely in a confusing range of packages. The Premium package includes a moonroof, a power tilt-and-telescoping steering wheel, driver memory settings, Bluetooth, an upgraded Bose audio system (of which the convertible gets a purpose-built version with headrest-mounted speakers), iPod connectivity and -- for the convertible only -- cooled seats. The Navigation package can be added to the Premium package and includes a hard-drive-based touchscreen navigation system with real-time traffic, voice-activated controls, a 9GB music server and a rearview camera. The Technology package, which is only available with the previous packages, includes adaptive cruise control and adaptive headlights. Additional options that are available with various trim levels and packages include four-wheel active steering, a rear spoiler and interior wood trim.

Powering all 2009 Infiniti G37s is a potent 3.7-liter V6 that growls with 328 horsepower and 270 pound-feet of torque. Base, Journey and G37x models come standard with a seven-speed automatic transmission featuring manual paddle-shift control and rev-matched downshifts. The Sport 6MT comes with an exclusive six-speed manual transmission. G37s are rear-wheel drive except for the new G37x, which is all-wheel drive.

In testing, an automatic G37 Journey sedan sprinted to 60 mph in a remarkably swift 5.4 seconds; the heavier convertible took a bit longer at 6.0 seconds. For G37s equipped with an automatic transmission, fuel economy rings in at an EPA-estimated 18 mpg city/26 mpg highway and 21 mpg in combined driving; Sport 6MTs have 1 mpg less across the board. The convertible loses an additional mile per gallon relative to its sedan/coupe equivalents in both city and highway driving, and the all-wheel-drive G37x registers 18/25/20 mpg.

The entire 2009 Infiniti G37 line comes standard with stability control, traction control, front-seat side airbags, full-length side curtain airbags and active head restraints for the front seats. Added safety equipment is included with the optional Technology package, which includes adaptive headlights and pre-crash seatbelts that use the cruise control sensors to detect an impending impact and then automatically pre-tension. Convertibles have standard pop-up roll bars.

In government crash testing, the G37 sedan was awarded a perfect five stars for frontal impact protection for the driver, as well as for side impact protection for all occupants. Frontal impact protection for the front passenger earned it four stars. The Insurance Institute for Highway Safety hasn't reported on the G37, but last year's G35 sedan scores should still apply. That car received a top score of "Good" for protection of occupants in both frontal offset and side-impact crashes.

The 2009 Infiniti G37's big V6 serves up thrilling acceleration, but we're not fans of the coarse noises it makes at higher engine speeds. We can't complain about the G's handling, however. This well-sorted Infiniti attacks curves with aggression and precision, yet it remains poised and compliant when driven over less-than-perfect pavement. Think of it as a world-class athlete in evening wear. Steering feel is commendable, particularly with the quicker of the two available ratios (standard on coupes and convertibles, optional on sedans). This sporty setup provides excellent feedback and a pleasant weightiness that builds progressively when cornering. The same cannot be said for the optional four-wheel active steering, though, which feels artificially light at the helm.

This year's new seven-speed automatic transmission is mostly praiseworthy. Quick gearchanges are at your fingertips via the steering-wheel-mounted paddle shifters, and downshifts are executed with precise throttle blips to match revs. In testing, however, we've noticed that upshifts, even when in Drive, aren't as smooth as they should be for this class of car. Even so, this year's automatic makes a strong case for itself versus the optional six-speed manual, which has a pleasing bolt-action feel through the gates but is hampered by abrupt clutch engagement.

The G37 offers user-friendly controls, excellent build quality and a handsome design -- the latter highlighted by such items as the car's leather-accented magnesium transmission paddle shifters and the Japanese "Washi-paper finish" aluminum trim (or optional wood trim). The front seats are comfortable and well-bolstered, and the available sport-styled seats offer even more aggressive bolstering, though they may be a bit too snug for larger drivers. Both the sedan and coupe/convertible feel like sports cars wrapped in a luxury car package, but the coupe and convertible, with seats that are mounted slightly lower than the sedan's, feel a bit racier. The optional Bose audio system is excellent, and the convertible's headrest-mounted speakers make it even better.

The G37 sedan offers ample space for rear passengers, with the exception of the narrow center seat, which is mounted rather high, severely compromising headroom and comfort. As expected, the coupe's and convertible's backseats are significantly more cramped than those of the sedan. The coupe's trunk measures a modest 7.4 cubic feet but the rear seatbacks fold down if more space is needed. The sedan's larger trunk accommodates 14 cubic feet of cargo and also includes a center pass-through for longer items. The convertible's trunk will accommodate two golf bags with the top up, but carrying capacity shrinks to about 2 cubic feet (think tissue box and not much more) with the top down.