The KB Pistons are lighter and that's the upgrade part of it ...but then you'll have to rebalance the assembly, though...you'll be removing weight and not adding, so it's on the cheaper side.
I think if I were you... I wouldn't change the Pistons unless I was going to over bore it.. like if I decided to put new bearings and everything in it... and the bores are out round ,for instance...cause then its a waste of parts.
