2011 Infiniti M56 vs. 2010 Mercedes-Benz E550 Comparison Test

You won't find a luxury sedan from every prefecture in Japan and province in Germany in this test — just the 2011 Infiniti M56S and 2010 Mercedes-Benz E550.

But this isn't some random pairing of business-class sedans. We're like sommeliers here at Inside Line, and this evening we bring you the two midsize luxury sedans with the largest available V8 engines (well, aside from the E63 and Cadillac CTS-V). The Infiniti M56S and Mercedes-Benz E550 have a combined 11 liters of engine displacement. If you were a good old boy, you'd know that's 672 cubic inches.

Even if you're not good or old, you learn the simple pleasure of low-end torque every time you plant the throttle in the 2011 Infiniti M56S and 2010 Mercedes-Benz E550. These sedans move out with the cool authority of corporate executives cracking the whip on the backs of middle-management slackers.

The Mercedes E-Class is a classic choice if you're looking to assert yourself and still drive around in something civilized. And the E550 just so happens to have won our last comparison of midsize V8 luxury sedans.

The 2011 Infiniti M56S, meanwhile, is an upstart angling for a promotion. This new M promises more sophistication and interior room than the outgoing M45. Yet it's also trying to make its mark as a sport sedan in a class that's rapidly losing interest in sport sedans, especially when it carries the package of equipment that makes it an S model. It's a lot to accomplish in one car, and an especially big task when you're up against a luxury sedan that always seems to have all its ducks in a row.

More Alike Than Different
Though the 2011 Infiniti M56 and 2010 Mercedes-Benz E550 couldn't look more different on the outside, we're struck by the similarities in their basic specifications. They're within 3 inches of each other in overall length, and they ride on nearly the same wheelbase and track. They weigh within 50 pounds of each other, which is to say they tip the scales at 2 tons apiece.

What the Infiniti's soft curves can't quite hide is that it's nearly 5 inches narrower across the shoulders than the square-jawed Mercedes. It's a consequence of the fact that the M56 is based on a Japanese-market Nissan designed to pack into urban landscapes with millions of people and apartment blocks.

So the Infiniti M56's cabin ends up feeling more snug and intimate than the Benz's open, airy quarters. It has a sporty identity, but there's a warmth to this design not seen in previous Infinitis. Though the M56 falls short in features, it cedes no ground to the E550 in overall cabin quality. Space is still more than ample in both, though, so it's a matter of your taste.

Mercedes Has More Stuff
However, this comparison test will indeed be won in the cabin. Amenities count for a lot in luxury sedans; if they didn't, we'd all be driving around in a stripped-down 3 Series. So for this comparison test, we've made the evaluation of features account for 20 percent of the final scores. The 2010 Mercedes-Benz E550 has a big advantage here — not because it has more shoulder room, but because it has more stuff.

The M56S and E550 might as well be a Tyrannosaurus and Louis XVI walking arm-in-arm into the sunset.

You'd absolutely expect the E550 to have more because it costs $71,955 versus just $64,435 for our 2011 Infiniti M56S (relax, pricing is weighted 20 percent, too). But it's not that simple, because the Benz comes with key items that you can't get on the Infiniti for any price.

Airbags are a biggie. Maybe you don't absolutely need the E550's driver and front-passenger pelvic airbags, plus a knee airbag, but you'd sure appreciate them in a major front-end crash. And with the Mercedes' standard TeleAid system, you'll probably get help fast, too. The E550's optional night-vision system, which delivers its clear black-and-white images to the central display, is also useful at helping you spot weird neighbors walking their dogs in the wee hours.

We also like that the 2010 E550 offers both a power-operated trunk lid (as an option) and a 60/40-split rear seat that folds perfectly flat. Every luxury sedan should offer these conveniences. Only coupe drivers are allowed to pretend that utility doesn't matter.

Probably the most critical feature in the Mercedes-Benz E-Class, though, is the little button on the console for its driver-adjustable adaptive damping system. The Infiniti M56S doesn't have one of these, and it rides stiffly on its 20-inch wheels no matter what. The E550, meanwhile, is easygoing and composed.

Open the Hood
Maybe you think the 2011 Infiniti M56S should just pack up and go home now. But owning a midsize luxury sedan is about more than counting up features and fussing over the ride. Sometimes it's just you in the car and you're just driving, and in these moments, the M56S is an interesting counterpoint to the overly refined E550.

Different personalities emerge as soon as you get on the throttle.

The 5.5-liter V8 in the 2010 Mercedes-Benz E550 is ridiculously smooth in its delivery, and you can feel the power building with the predictability of a linear equation. The Benz V8 is also quite at ease at high rpm. So even though its 382 horsepower peaks at 6,000 rpm, this 5.5-liter is happy to sustain its output all the way to the 6,400-rpm redline. Torque plateaus at 391 pound-feet from 2,800-4,800 rpm.

There's little question that the 5.6-liter V8 in the 2011 Infiniti M56S is a response to the always respectable Mercedes V8. It's comfortably over the 400-hp threshold with 420 hp at 6,000 rpm and 417 lb-ft of torque at 4,400 rpm. But this direct-injected engine has a more explosive power delivery than the Benz delivers.

Partly, this is due to the fact that the throttle map isn't quite sorted out to our liking. Response is unnaturally soft off idle, and then the M56S barrels ahead as if it has been smacked in the rear with a giant mallet.

But you also get the feeling that Infiniti's 5.6-liter wants to flex its muscles for you. There's a more palpable sense of athleticism as the engine revs. This V8 has business to take care of at high rpm and it wants you to feel that.

Now We Get Down to Business
Both Infiniti and Mercedes have settled on seven forward gears for their V8 luxury sedans, and of course, both automatic transmissions drive the rear wheels. Gearing is similar, and with two overdrive gears apiece and fairly tall final-drive ratios for optimal fuel-efficiency, both engines are loafing below 2,000 rpm at a 70-mph cruise.

However, the transmissions behave differently when you start making bigger demands. Here again, the E550 aims for smoothness above all else. Its seven-speed has Comfort, Sport and Manual modes, but this transmission really just wants to be a good automatic. There's no rev-matching on downshifts, but the seven-speed always seems to be in the proper gear without calling attention to itself.

The Infiniti M56S, on the other hand, wants your attention. It has Normal, Sport and Manual modes (plus torque-neutering "Eco" and "Snow" modes), and it serves up zingy, rev-matched downshifts. Leave it in Sport mode and it won't let you down on a mountain road. Those throttle blips are fun going into a turn, and the transmission lands you in the heart of the engine's power band when you're powering away from a corner apex.

Curiously, the M56S's seven-speed is sometimes a bit slow with upshifts (glacially so in Manual mode), and this, along with its funky throttle map, keeps the car from being significantly quicker than the E550.

The Infiniti hits 60 mph from a standstill in 5.2 seconds (4.9 seconds with 1 foot of rollout like on a drag strip) versus 5.3 seconds (or 5.0 seconds with rollout) for the Mercedes. That margin holds through the quarter-mile, with the M56S crossing the line in 13.4 seconds versus the E550's performance of 13.5 seconds. But the M56S's 106.1-mph trap speed, versus 104.8 for the E550, suggests the Infiniti is indeed leaving some performance on the table.

Sport Sedan vs. Luxury Sedan
Don't look for the 2011 Infiniti M56S to pull any punches on back roads, though. It wants to be a sport sedan, and in most respects, it is exactly that. Think about what the BMW 5 Series used to be and you'll have an idea of how it feels.

Setting up for a corner brings visceral joy. It feels like you can just stand on the brakes (upgraded via the Sport package and dealer-installed R-spec brake pads) repeatedly, and they'll still bite hard. In the end the M stopped from 60 mph in 112 feet at our test track and, by the seventh stop, it was still doing it in less than 114 feet. The big 245/40R20 95W Bridgestone Potenza RE050As live up to their reputation for big grip, too.

You sense that grip as you add steering input and you delight in the feedback and the heft in the wheel, and though the M56S's steering feels heavy, it never feels too heavy for the character of the car. The M turns in sharply and with minimal body roll. If you're brave enough to turn off the stability control, you get a little tail-out attitude but nothing too scary.

The M56S slaloms at 66.8 mph, which is faster than a 2009 BMW 550i (64.9 mph), though much slower than the supernatural E63 and CTS-V. It's good for 0.88g on the skid pad, so it's right in line with the 2009 550i.

Alongside the athletic Infiniti M56S, there's the Mercedes-Benz E550, which isn't interested in doing tricks for you.

The E-Class has light, accurate steering, but it doesn't say a whole lot and, really, there's not much to say. Its 245/45R17 99H Continental ContiProContact all-season tires don't have much grip. Understeer is what you notice through corners. The E550 goes through the slalom at only 62.8 mph and manages just 0.81g on the skid pad.

You also notice the brake pedal's long travel, yet consistently linear response, which is the safe strategy for autobahn emergencies in Germany. Said response is also consistently mediocre, though, because the tires are mediocre. The E550's best 60-0 stop is 125 feet.

The Mercedes by Three
For all the M56S's dynamic superiority, it's hard for us to tear into the 2010 Mercedes-Benz E550 for not being much fun. This is a luxury sedan without the theatrics. It's blissfully smooth in every respect, from the way its transmission shifts to the way its suspension absorbs a bump, and it is loaded with both leading-edge technology and old-fashioned conveniences.

Since all of three points separate the E550 from the 2nd-place 2011 Infiniti M56S, there's a compelling case for spending your money on a real sport sedan. In all the ways that the Mercedes feels sterile, the Infiniti feels lively. The M is the sort of car that you look for opportunities to drive by yourself, and that's not something we'd do with an E550.

Personal taste is a big factor in choosing one of these V8 sedans. But don't take too long to make your selection. With tougher fuel economy standards coming, the 2011 Infiniti M56S and 2010 Mercedes-Benz E550 might as well be a Tyrannosaurus Rex and Louis XVI walking arm-in-arm into the sunset. They won't get to keep their tasty V8s forever.

The manufacturers provided Edmunds these vehicles for the purposes of evaluation.