i not sure high performance pistons have a tighter clearance, why would you? Friction would increase...it could be to reduce blowby, but your choice of rings and breather system on a high performance option would cover this...
im no engine builder but i heard that higher grade alloy in high performance pistons that handles the heat better by not expanding as much as a standard piston so a tighter clearance can be achieved that could be bullocks but i did read that somewhere
