I wouldnt dig on porcelain, but I'm old-timey, glass and plastic dont belong in an engine, and billet pistons are probably much more practical, especially since they use a lower compression ratio anyway due to expansion. I have a lot of confidence in Mercedes and their engine I'd be willing to bet 450-500 HP is a good number to be at the end of reliable and even then gas mileage is like under 10MPG. But I doubt thats an issue if you're performance tuning something as far as it goes. The Sl's purdy heavy but the CLK aint too bad, thus, 450 is gonna make it fly, i think the DTM only have like 420? Not sure, but its a plenty. It's just theres a lot of little things, which is why the good machine shop is a must. Also, If you're going all out, a manual trans. out of a BMW M3,5 would be a good idea, since its a Getrag I believe. (unless you dig on automatics). Whatever you do in the end take pictures