Pistons are normally overdesigned to take more than it suppose to take. Up to a certain extend of course. Double metal gasket can be risky as there are more possibility for the water and oil to mix due to increased chances of uneven head tightening problem.
If skimming pistons are done nicely, problem can be less than a double metal gasket. I've seen ppl using double carbon gasket. But carbon gasket are compressible and metal gasket aren't.
Advantage & disadvantage??