By James R. Healey, USA TODAY
Infiniti's overhauled M37 V-6 sedan is a brilliant blend of style, personality, comfort and performance. Of course, for $50K or so, it ought to be pretty good. But it's extraordinary even when price is considered.
The M56 V-8 model, though ...

The M56 rear-drive test car earned our unyielding enmity by including an options package that had lane-departure warning. Stray from the very center of the lane and: beep, beep. The lane warning had an off switch, but you had to use it each time you started the car. Infiniti says you can turn off the feature permanently using a control accessed by the navigation screen.

Best part of that feature is that it's optional. Unless you drive perfectly centered down the marked lanes — and here's a bet that nobody really does — you'll find it bothersome. Using the turn signal to telegraph your intention to switch lanes overrides the departure warning, a pleasant display of common sense.

We emphasize the aggravation of the lane warning system because it symbolizes a larger issue: an error in presentation, or perhaps simply an irony. The lower-price M37 is such a well-done, satisfying machine (based on our time in a preproduction rear-drive model) that the much higher-price, well-optioned M56 seemed overdone, gratuitous, crass.

The M56 test car's window sticker of $67,410 included such options as "Japanese white ash wood trim with genuine silver powdered accents." Oh, please. Yes, it seems impressive in those ads, but no, it didn't look especially wonderful.

The M37 was strong evidence that, still and forever, less is more. (Well, maybe not when it comes to money. Or vacation.)

The 3.7-liter V-6 and the 5.6-liter V-8 both offer optional all-wheel drive and, if you're so inclined, enough ain't-we-cool options to satisfy most folks. Note that the V-6 runs just $460 more than the 2010 model, while the V-8 is a hefty $5,410 more. (Those include a $10 increase in shipping charges.)

The M56, in addition to the overwhelming V-8 engine, comes with these standard features that cost extra in the M37: heated and cooled front seats; Bose stereo; hard drive to store CD or MP3 tunes you play in the car; navigation system; voice control for audio, navi and vehicle info systems.

The M37 test car had no official price sticker because it was not meant for a showroom. Infiniti portrayed it as at the lower end of the price and features spectrum, which would be roughly $48,000. Never mind. If it would have had the optional AWD — making it an M37x — the tester would have been about the best daily-use buggy imaginable.

The only real complaint was the seven-speed automatic transmission. Should have been a high point. But there was too much going on. Shifting, or not, when you expected the opposite. Intrusive. Not so in the M56, though that one's gearbox wasn't really world class, either.

The 330-horsepower V-6 (up from 303 hp in the 2010 model) remains laudable. Strong, smooth, engaging, polite. Makes you wonder, why spend more for the V-8? Sure, more power is terrific. And the 5.6-liter V-8's 420 hp (up from 325 hp in 2010) rockets the car on demand. But the M37 has more than enough oomph and delivers it without the sometimes wearying drama of the V-8.

Both testers had a nice balance of driving ease and handling crispness. Brakes came on right now when the pedal was nudged. Steering seemed to stay pointed straight ahead until the driver signaled a change via the steering wheel, which felt uncommonly pleasant because of its leather covering and the size and shape of the rim itself.

The M is considered a midsize car (though on the big end of that category). It had enough room to seat five, but the center tunnel was so tall that it limited the middle rear spot to a very small person. The other slots were comfortable and plenty roomy.

Notable details:

•Remote key remembered stereo, navi and climate-control settings, in addition to the usual seat, steering wheel and mirror positions.

•Small lights on the underside of the exterior door handles illuminated as you approached the car. Classy, and good for avoiding puddles or dog leavings.

•Pull-down center rear armrest yawned open to provide a just-right holder for your Snarf Shack Quad Burger and Triple Fries, plus a couple of drinks. Surprising how many fold-down armrests lack such useful space.

For Infiniti's attention to that detail, the kids (and their dad), say, "Thanks."

•Multiple settings on a console knob tailored the drivetrain's response. You could choose among eco (of course, there'd be such a setting these days), snow, normal, sport. Eco let you know you're pushing the gas pedal hard, hoping to dissuade you. Snow started in a higher gear to avoid wheelspin. Sport improved responsiveness by holding the transmission in lower gears longer. Zippy, yes; fuel-thirsty, you betcha.

Normal worked just fine in both testers, thank you very much.

The Infiniti M has long been a personal favorite, a car to consider if you had to keep it a long time. The 2011 M37 remains so. But the M56, especially the loaded version, not so much. That one seems appropriate for those who think too much is never enough.

About the 2011 Infiniti M37/M56

What? Overhaul of the brand's midsize, four-door, five-passenger sedan, available with rear-wheel drive (RWD) or all-wheel drive (AWD), which is designated "x." Slightly longer, wider than previous model and considerably more powerful and fuel-efficient.

When? On sale since spring.

Where? Made in Japan.

How much? M37 RWD starts at $47,125, including $875 shipping. M37x is $49,275. M56 RWD is $58,425. M56x is $60,925.

•V-6 model is $460 more than 2010 version (including a $10 boost in the shipping charge). V-8 is a hefty $5,410 more.

How powerful? Much more so than 2010. M37 has 3.7-liter V-6 rated 330 horsepower at 7,000 rpm, 270 pounds-feet of torque at 5,200 rpm. M56: 5.6-liter V-8, 420 hp at 6,000, 417 lbs.-ft. at 4,400.

•Seven-speed automatic is the only transmission.

How big? 194.7 inches long, 72.6 in. wide, 59.1 (RWD) or 59.6 (AWD) in. tall, on a 114.2-in. wheelbase.

•Weight: 3,858 to 4,224 lbs.

•Passenger space, 103.6 cubic feet. Trunk, 14.9 cu. ft. Turning circle diameter: 36.7 ft. (RWD), 37.4 ft. (AWD).

How thirsty? M37 (RWD) rated 18 miles per gallon in town, 25 mpg on the highway, 21 in combined city/highway driving. M37x: 17/24/20. M56: 16/25/19. M56x: 16/23/18.

•Trip computer in M56 regular-production test car registered 19.2 mpg (5.21 gallons per 100 miles) in mix of suburban, freeway driving.

•Holds 20 gallons. Infiniti says premium is required, not merely recommended.

Overall: M37 is a sweetheart. Pricier M56 seems a bit overdone.