The luxury sedan game is a tough nut to crack. When someone is ready to pay $60,000 or more for a car, they expect a certain level of refinement and prestige. Traditionally, those levels have been best met by cars from BMW and Mercedes-Benz. The 2011 M56 is the latest attempt from Infiniti to crack that nut, taking the more sport-tuned formula of its previous M45 sedan and applying a more striking design and up-to-date technology to the mix.

Along with its V6-powered sibling, the new M37, the 2011 Infiniti M56 is a midsize luxury sedan available with rear-wheel drive and all-wheel drive. As before, the M caters to those buyers who are looking for an involving and rewarding drive from their luxury car, and this Infiniti certainly won't disappoint. Although the M37 likely features all the power you'd ever need, the M56 is for those who desire a whole lot more.

With a 5.6-liter 420-horsepower V8, the M56 socks it to virtually every competitor in its class. Ten years ago, this would've been the stuff of an M5 or AMG E-Class, and today it's still a thrill to plant your foot into the carpet. However, not only has the M56's engine grown larger than its M45 predecessor's, but the entire sedan has hit the gym as well. Its curvaceous, muscular styling conceals a greater width and length, but also a shortened height to give it more aggressive proportions. The interior dimensions haven't changed much, which is fine since the M was already one of the more spacious vehicles in the class.

It was also one of the most technologically advanced at one time, and that distinction has once again returned. The number of comfort, safety, performance and entertainment features that inhabit the standard and optional equipment lists would make "War and Peace" look abridged. Not only are new items like the Forest Air purification system and Active Trace Control (which enhances the transition from braking to acceleration through corners) been added, but previous features like the navigation system have been improved. Perhaps best of all, many of these features reside in a cabin that is now more attractive and better made.

Still, the 2011 Infiniti M56 isn't without faults, the most notable being a firm ride that can be too frenetic at times for some luxury sedan buyers. There are also a lot of worthwhile V8-powered competitors to consider even if they're generally more expensive. The 2011 BMW 5 Series has also been redesigned for 2011, and although it's not as fun to drive as the M, it's more well-rounded. The 2011 Mercedes-Benz E-Class was redesigned last year, and is once again the standard-bearer for those who value comfort and refinement over a sporty driving experience. The 2011 Jaguar XF is also worth considering given its posh interior and slinky styling.

However, we can't help getting around the fact that the 2011 Infiniti M56's biggest competitor is its less expensive sibling, the 2011 Infiniti M37, which also boasts more horsepower than its V6 competition. Many buyers are likely to think the M56 is overkill, and there is historical precedent to back up that observation, as the old M35 outsold the M45 by almost six to one. For that one, however, overkill is likely to be a sought-after attribute, and with 420 hp, the M56 certainly has the overkill to help crack that luxury sedan nut.

The 2011 Infiniti M56 is a midsize luxury sedan available in a lone trim level, though there is an M37 discussed in a separate review that is essentially the same car but with a smaller engine and less standard equipment.

The M56 comes standard with 18-inch wheels, automatic bi-xenon headlights, foglights, power-folding heated mirrors, automatic wipers, a sunroof, keyless ignition/entry, dual-zone automatic climate control, leather upholstery, heated and ventilated eight-way power front seats, driver memory functions, a power tilt-and-telescoping steering column, a heated steering wheel and an auto-dimming rearview mirror. Also standard are a rearview camera, Bluetooth, a navigation system (includes voice control, real-time traffic and real-time weather) and a 10-speaker Bose stereo with a CD/DVD player, auxiliary audio/visual jack, streaming Bluetooth audio, iPod interface, satellite radio and digital music storage.

The Deluxe Touring package adds a power rear sunshade, an in-car air purifier, upgraded leather upholstery and interior trim and a 16-speaker Bose surround-sound stereo. The Sport package (not available with all-wheel drive or the Deluxe Touring package) adds 20-inch wheels, summer tires, sport-tuned suspension and brakes, four-wheel active steering, sport seats and steering wheel, and unique exterior styling elements. The Sport Touring package adds the surround-sound stereo, air purifier and power sunshade to the Sport package. The Technology package includes adaptive cruise control, lane departure warning and prevention system, blind-spot warning system, forward collision warning system, adaptive headlights and the "eco pedal" that provides the driver feedback to encourage fuel-efficient driving.

The 2011 Infiniti M56 is powered by a 5.6-liter V8 that produces 420 hp and 417 pound-feet of torque. Rear-wheel drive is standard, but the M56x features all-wheel drive. A seven-speed automatic transmission is standard and includes manual override shift paddles and four different shift modes (Standard, Sport, Snow or Eco).

In performance testing, the M56 goes from zero to 60 mph in a rapid 5 seconds. EPA-estimated fuel economy is 16 mpg city/25 mpg highway and 19 mpg combined with rear-wheel drive, while the M56x returns 16/23/18.

The M56 comes standard with antilock brakes, stability and traction control, front side airbags, side curtain airbags and active head restraints. Included in the Technology package are a lane departure warning and prevention system, blind-spot warning system and a forward collision warning system with intelligent brake assist. In Edmunds brake testing, an M56 Sport came to a stop from 60 mph in a very short 113 feet. The non-Sport model took only a few feet more.

In the government's new, more strenuous crash testing for 2011, the M56 earned an overall rating of four stars out of a possible five, with five stars for overall frontal crash protection and five stars for overall side crash protection.

The 2011 Infiniti M56 is a big car, but it drives smaller than you might think. Its steering weights up less abruptly than in other Infiniti and Nissan sedans, and it exhibits a willingness to change direction that is downright feline for its size. The 5.6-liter V8 produces the sort of power that used to only be available in sedans badged M5 and AMG. Putting your foot to the floor will unleash a rush of acceleration that'll get you grinning. In our initial drive, though, we found the big V8 dulled the car's handling slightly when compared to the M37.

Yet if a V8 is a must and you desire an even more sharply tuned luxury sedan, the Sport package brings with it various performance upgrades that put the M37 in a position to embarrass its European rivals. However, the combination of sport suspension and 20-inch wheels further spoils the M56's already firm and occasionally rough ride quality. We like a sporty car, but the M56 tends to be a little too frenetic, even for our tastes.

Infiniti has given the new M56 a top-notch cabin design and high-quality materials. Like the exterior's styling, the flowing design has a tautness to it, as if there were muscles trying to bulge their way through the many tactilely pleasurable surfaces. If you select the Deluxe Touring or Sport Touring packages, the seats are upgraded with diamond-quilted leather and contrast piping, unique wood trim, a faux-suede headliner and enhanced materials added to most primary touch points. In total, the M56 has an interior worthy of taking on its established European rivals.

The cabin is quite roomy, offering generous space for all occupants and a relatively tall greenhouse that provides good outward visibility. As for technology, it's hard to think of a rival that betters the M56 for all the available entertainment, comfort and safety technologies that can be had once you check all the options boxes. In particular, Infiniti's navigation and audio interfaces are some of the most user-friendly in the business.