Before you jump into heavy disc thinning remember that discs brakes also serve as a heat sink and that factor is directly related to disc mass. so lighter is not necesseraly better, surely not in tracks with heavy braking bits.
I've been running 4.5mm discs on a lightweight CB500/4, wouldnt go under 5mm on a 750 IMHO. Havent done any heavy drilling either, just a good pattern to keep all the pads clean, certainly have not "swiss cheesed" them
My 0.02$