Like every current car-based Infiniti product, including the outgoing M, the new M37 and M56 sedans are based on Nissan‘s advanced FM (Front Midship) rear-drive, unibody architecture. That means the engine is positioned back behind the front wheels’ centerlines, and the suspension is all-independent with double wishbones at each front corner and a multilink system on coil springs in the back. All that is familiar, mostly carryover, stuff. Even the wheelbase is unchanged at 114.2 inches.

The new Infiniti M is overall about 2 inches wider than before with the front track widening by 1.4 inches and the rear by 0.8 inches. All the sheet metal is new with the super curves Infiniti M56 Accessories has adopted as its current design theme. It’s not the sort of look that’s going to win universal praise, but it’s clearly unique and handsome in its own way. The M’s additional size is somewhat offset by using aluminum to skin the hood, trunk lid and doors.

Those swoops continue inside the M with a dashboard shaped as if it were a wave cresting at the base of the windshield and door panels. The interior materials are of the high quality expected of vehicles in this lofty class, and some elements, like the matte-finish wood, are almost profoundly gorgeous. Best of all, the interior feels roomier than before with decent legroom in the back.

M37x prototype is powered by a 327-hp, 3.7-liter V-6 with 269 pound-feet of torque, more or less identical to that found under the hood of the G37 sedan, and fitted with all-wheel drive (as is the M56x). As with its smaller FM-platform mate, the V-6 and its accompanying seven-speed automatic are a smart match. The M37’s lower weight and delightfully natural steering—especially compared with the M56 Sport’s four-wheel-steering system that varies the steering ratio and can turn the rear wheels in the same direction as the fronts by as much as one degree—made it our favorite by far.

But that could change by the time the new Infiniti M hits U.S. dealerships in late March or early April. (Infiniti’s first hybrid, based on the V-6 M, is to follow a year later.) According to company spokesman Kyle Bazemore, numerous changes have been made to the M56 that address our chief areas of concern: V-8 exhaust note, throttle tip-in, and shift mapping. About the four-wheel steering, however, Bazemore was uncertain.