how much weight variation are we talking grams?.. I had this discussion with a low budget racer, he told me "most of that stuff is in the ballpark with each of the others" now keep in mind this dude want picky, he just figured 8 stock rods and 8 pistons, if they are the same ...how off can they be? i would think though if you are going higher than recommended stock RPM (racing) it would become very important to the balance.