Comparison: 2012 BMW M5 vs. Mercedes-Benz E63 AMG vs. Porsche Panamera Turbo S

One day, three cars, twelve doors, and 1,660 horsepower. Discuss
You could almost feel sorry for anyone positioned to spend a six-figure sum on a "family" four-door. If there is such a thing as the world's best car, it probably dwells among this sub-breed of hyper-achieving midsize sedans: one moment, luxury conveyances for at least four occupants; the next, candidates for sub-eight-minute bragging rights round the Nürburgring Nordschliefe. It almost seems too good to be true that any cars like these exist at all, let alone that there are so many to choose from.

BMW, Cadillac, Jaguar, Mercedes and Porsche all build family-sized four-doors with outputs north of 500 horsepower. Who could possibly pick only one?

For us, the next best thing to having one to keep would be to have all five for one week. Regrettably, even the vast resources of MSN Autos couldn't quite make that happen. So we settled for one day, three cars, and multiple laps of some of our favourite Ontario driving roads. We're still not complaining.

BMW's M5 is arguably the grand-daddy of the übersedan breed, and has just entered its fifth generation, based on the F10 5 Series that was all-new for 2011. The Mercedes-Benz E63 AMG has been around a while, but received a new engine for 2012 that slashed fuel consumption even as it raised performance to an even higher plane. Completing our set, the Porsche Panamera was represented by the Turbo S, with the "S" representing a new-for-2012 performance package added to the already rabidly rapid Turbo.

For sure, nobody looking to drop $100,000 on a midsize sedan would be swayed by the $1,800 difference between an E63 (base: $99,700) or an M5 ($101,500). But what about twice the price? That's the size of the "price walk" to the $200,300 asked for ultimate Porsche sedan. Still, we make no apologies for including the Porsche in this match. In size, features and intent it belongs.

Besides, is it such a stretch to suggest that among the one-percenters who can afford a $100K car, many of them could equally easily afford a $200K car? Closing argument: the regular Panamera Turbo would also be a contender in this company and it starts at "only" $158,500.

For some time, Audi, BMW and Mercedes have observed a "gentlemen's agreement" to govern their sedans' maximum velocities to 250 km/h. Among this threesome, however, only the M5 toes that line. Our E63 test sample came with the AMG Performance Package (APP), which raises the governed limit to a claimed 300 km/h. The Porsche ... well, Porsches do what Porsches do, and in the case of the Turbo S that means 306 km/h, limited the old-fashioned way, by aerodynamic drag.

Oddly, though, all three automakers are largely in accord about how much horsepower is sufficient for an übersedan. Not sure what's significant about 550, but that's the precise number of pferdestarke claimed for both the Mercedes and the Porsche (though in the case of the former you need the APP to get it: 518 hp otherwise). Our tech sheet for the M5 says 560 hp, but that's a European rating: expect a little less (550, perhaps?) by our SAE net ratings.

These overdoses of omnipotence are all delivered by twin-turbocharged V8s. In case of the Bimmer and the Benz, said V8s represent downsizing in the name of fuel economy: they respectively replace a 5.0-litre V10 and a 6.2-litre V8, both naturally aspirated, in previous versions of these cars.

The engines do break ranks in displacement, ranging from the M5's 4.4 litres through 4.8 in the Porsche to 5.5 in the E63. Maximum torque outputs diverge accordingly: an even 500 lb.-ft. for the M5, 516 for the "regular" E63 and 553 lb.-ft. for the Turbo S. As tested, however, the latter two each rated 590 lb.-ft. courtesy of APP on the E63 and temporary over-boost on the Porsche.