IMO if you run fully ported heads and you are going to stay m90 the XPZ is your best bet if you dont want to go full XPZ a S1X or XP will also make good power. Stage 3 and 4 cams tend to like a larger power adder to be worth it. However if you do plan on running nitrous you may be able to get away with a bit bigger cam. The problem you run into here is that a M90 loves a intake bias cam and a nitrous setup will love a exhaust bias cam. So you will have to make that choice.