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The horsepower race is on, again! BMW's M5 was king of the hill with its hi-revving 507hp V10 until Mercedes released the E 63 AMG with 511hp. Surely only just a few extra horsepower but it still counts as the German premium marques compete with each other.

Now, there’s a new kid in town - the twin-turbo V10 Audi RS 6. With its massive 580 horsepower under the hood, it is speculated that Audi has understated the true horsepower figure of 600hp. How long will the RS 6 hold the throne? Well, most likely until the new Mercedes E 63 AMG is released in mid 2009 with a unconfirmed 544hp, however, it seems based upon these latest spy photos that BMW may have a trick or two planned.

Evidence shows BMW is preparing a slightly more evil version of the M5, and this time it appears to be twin-turbos! According to the photographer who snapped this M5 prototype, the engine sound was different from the usual M5. In addition, clearly visible are the extra air intakes cut in the front bumper. However, take a closer look inside the lower air duct openings on the sides of the front bumper and you'll notice a verticle flap which redirects the air flow into what appears to be sitting behind an intercooler for a turbo.

And while we are on the subject, why not speculate about the testing of an 7 Series based M7. The pictured 7-series prototype has shows a few clues beyind the normal 7-series prototypes that we have been seeing lately. Check out the big air scoop in the hood and two smaller air outlets at the back edge of the hood. Could this be the sign we have been hoping for? It’s known that the new 7 series will be sportier and more fun to drive, so why shouldn’t there also be an M7, after all to compete with Mercedes' S 65 AMG and Audi's potential RS8?