Acceleration impresses with either V6 or V8 power. A rear-drive M35 scurries nicely, delivering abundant around-town zip and highway power. All-wheel drive adds 180 pounds to car weight, but feels little different. Overall, the M35 is so adept that extra thrust of the M45 is not a compelling draw. That said, the M45 is fast by any measure; a test example accelerated to 60 mph in 6.0 seconds. With either engine, the transmission sometimes pauses indecisively on downshifts, but its manual-shift feature is quicker than most. Fuel economy is about as expected in this league. A test M35 averaged 16.4 mpg in city/highway driving, while an M35x averaged 17.4 mpg with more highway use. Test M45 sedans averaged 16.0 mpg in city/highway driving, and 18.8 to 19.1 mpg in mostly highway use. Infiniti recommends premium-grade fuel for the M35, and requires it for the M45. On the road, all M sedans are firm and composed, but the base M35 absorbs bumps best. The all-wheel-drive M35x has tauter suspension settings. Sport models have stiffer suspensions than base sedans, plus low-profile tires that produce some jarring when encountering ruts, and jiggles on grooved pavement. Confident and balanced handling is accompanied by minimal cornering lean. Sport models have impressive grip in fast changes of direction, though the effect of the Rear Active Steer system is hard to detect. Steering on all models is precise and secure on-center, but heavy and slightly unnatural feeling in turns. The M35x has rear drive manners on dry surfaces, with automatic transition to AWD upon wheelslip (50/50 front/rear torque split can be locked in via a console snow-mode button). Strong brakes on all models are easily modulated. Quietness depends on the model and road surface. These sedans deliver fine supersession of wind rush and engine/exhaust note, but M35x and Sport models thump over cracks and bumps. Sport models roar and whine on coarse surfaces. Bright, clear gauges greet the driver. Most controls are logically arrayed on a keyboardlike shelf, but are numerous enough to demand study. Some are a reach away, and sunshine neutralizes indicator lights. Closer to the driver are traditional audio knobs and buttons. Nissan/Infiniti's navigation system is exceptionally easy to operate, and voice recognition responds accurately to command keywords. The available lane departure system beeps a lane-change warning unless the turn signal is used; it can be shut off, but may seem gimmicky to some drivers. Keyless ignition is a convenience, and the fob stows cleverly in a dashboard port (a "No Key" message flashes if the fob leaves the car while the engine is on). Trim of satin-finish wood or real metal, precision switchgear, and plenty of soft-touch surfaces creates an inviting cabin ambience. Front space is generous, on supportive seats that are astutely bolstered. The power tilt/telescopic steering wheel helps fine-tune driver position. Thick pillars partially obscure over-the-shoulder visibility. Although the backseat is firm and nicely contoured, its cushion is not long enough for best thigh support. Knee clearance is fine, but toe space tight with the front-seat height lowered. The middle-rear rider straddles a tall driveline hump. Trunk volume is ample, and lid hinges don't intrude. However, a short aperture means drawerlike access. Inside the car, storage space is sufficient.

Value for the Money
This impressive sedan is a credible competitor to such class benchmarks as the Acura RL, BMW 5-Series, and Mercedes-Benz E-Class. Generously equipped in standard form, delivering convincing performance and available with all-wheel drive, the Ms are Best Buy alternatives to these and other rivals, at each price point on the premium midsize spectrum. Infiniti Ms hold their value reasonably well, so used-car prices tend to be a bit high.