The M sedan didn’t start out as Infiniti’s flagship, but it inherited the mantle when production of the Q ended in 2006. With the third generation, the M has everything befitting the marque’s top spot, especially the 420-horsepower M56.

Infiniti purposely broadened the power gap between the V-6 M37 and the M56 by using a new, direct-injection V-8 that bests the V-6 by 90 horsepower. The old M35 was within 22 horsepower of the M45 and boasted a seven-speed transmission—why buy the V-8? With 330 horsepower, the M37 is by no means wanting for thrust.

The really sweet thing about the M? The only difference between the 37 and the 56 is the engine—either one can be built with the same option packages. When when you opt for all-wheel drive which can’t be had with  Sport or Sport Touring.  For the sake of brevity here, you can sort through details and how they mix and match at Infiniti’s Web site. The automaker provided several variations of the M for us to drive.

M37

At first the steering felt a little heavy, but like a new suit that takes a few minutes to become comfortable the feel of the car quickly came right. Handling is responsive with no understeer, but you know you’re driving a 4,000-pound automobile. At no point did it feel like the car needed to be wrestled through corners, but M’s feathers aren’t ruffled by late turn-in and the car took to the desired line.

The V-6 has enough torque to move the car off the line with authority. If you’re in the mood to cruise, put the transmission in D and you can lope along without a care. Switching the Drive Mode from normal to Sport brings on snappier throttle response and gear shifts. Want more control, put the selector in manual shift mode. You can run up through the gears, dancing at redline with the seven-speed transmission executing your choices without hesitation. The M’s gearbox rev matches downshifts so you can always stay in the engine’s power band. It could only get better with a dual-clutch transmission. Yes, Infiniti that’s a hint.

The M’s brakes have no trouble bringing the car down from speed. Brake pedal is firm, with no grabbiness at low speeds. Under hard braking, there isn’t even a hint of drama, testament to the modern ABS and electronic force distribution system.

Wind and road noise are well subdued, but not so much that you lose touch with the road. Seats are supportive enough for spirited driving and comfortable enough for long stints. We drove an M37 with the Technology Package, which includes Blind Spot Detection and Lane Departure Warning. The former illuminates a lamp next to the side-view mirrors—nice information even if you aren’t changing lanes. The latter uses a warning chime, which could get annoying after a while.

M56

Ah, throaty, delicious V-8 power, the kind that lets you know it heard you ask for speed by launching from a stop or rocketing past the slow-moving motorhome.

We drove the Sport Package, which adds bigger brakes, stiffer springs, dual-piston dampers, four-wheel steering and 20-inch wheels and tires. The M56 shares the same transmission as its little brother, so when you want to joust with a twisty road, turn the Drive Mode dial to Sport, put the gear selector in manual mode and prepare to do battle.

Can you the M dive-bomb corners like a 2,000-pound Lotus? Of course not, but you can trail-brake through corner entry and the car sets up nicely. At mid-corner you can accelerate aggressively right through the exit. Keep pushing the accelerator and objects in the rearview mirror get very small, very quickly. While you can feel the weight in corners, the car’s electronics keeps it all well behaved.

While the M56 rockets up to freeway speeds and beyond, the Sport Package’s bigger brakes bring it back to Earth quickly and confidently. You will not reach the car’s limits on public roads legally or sanely. In short, the monstrous side is always at your beck and call.

Conclusion

BMW took touring sedans in a sporting direction nearly four decades ago and still sets the benchmark. Hear in the 21st century, the Roundel brand is hardly alone. Audi, Acura, Lexus, Infiniti, Mercedes-Benz, Cadillac, and now Buick, share the road. Infiniti’s M is among the few that can claim full membership in the club: sporty, not ill-mannered; connected, not insular.

Pricing