[Phast SVX]

ok so heres the deal(dilemma), i am purchasing a motor from a yard shortly here. I dont really want to lower the compression, especially if i never go FI, but theoreticlly i wonder much much i have to looser by slightly lowering compression and going with their forged pistons. I hate emiling them so much, is there a mathmatical calcuation or are their too manyother variables?
phil