Piston slap, as said above by fatz, is only really noticeable if the machinist doesnt know what he/she is doing....
Joel and myself went for twice over std. bore (40 thou) and use Wiseco forgies...they do a great job, and i have trouble hearing any slap, but Joel reckons he can hear it a tiny amount.
Oh yer, one of the guys in the rb30 thread makes a 4wd sump adaptor, and the exhaust doesnt need modding all the time. Joels exhaust bolted straight up.