BMW or any brand for that matter will not sell a car that is faster than a higher end car.
Well that's not true,...they will, but they won't advertise it.
The M6/M5 are the M division's cream of the crop. BMW does not want the rich bastards buying M5's and 6's to think that daddy's spoiled little 23 y/o brat in the M3 that cost 20 grand less can out run him. So they advertise slower times for the M3, to place it in the correct market segment.
Road and track got the M5 to do 0-60 in 4.1, now that's ridiculous. But, it's officially listed as a 4.8 car.
My guess is the E92 M3 will be in the 4.2 range, like the 360 Modena.
Don't worry guys, the E92 WILL be faster than the E46. But it's not a competition, besides older brother E46 taught E92 everything he knows.