i just read a buyer guide for M3's in Bimmer magazine.
the problem with the blown engines is the 8k rpm redline. that is because the marketing dept wanted it that high for sales. so engineers worked long and hard to get it to be stable at that engine speed, but of course, it wasnt really meant for 8k.
the M roadsters have the same S54, but the redline is 7600 rpm, and they never had a blown engine. so keep it under 7500 rpm i would say