I shoot for and have seen the best results at a target of .040, I've run as tight as .036" on a 12:1 combo; To my mind you alsos have to be mindful about piston rock and remember the rock at TDC effects the quench area oppositely on each bank of a V8. I would consider anything above ~.045" the same as "no quench" and this applies only to steel rod combos.