[ptack]

For all of the speculation I would say the only certainty is that the performance of the M3 and 5 will have to be in line with the performance of its rivals. If Audi, Lexus and Mercedes are all selling cars that keep raising the bar, it would be suicide for BMW to walk away and say, "well we'd rather be slower, but more economical". If BMW can engineer category leading performance with smaller engines, then kudos to them. The bottom line (literally) is that these cars must be competitive.