Another source of miniscule power "loss" would be the dead space above the top ring. With a piaton below deck, the ring is down further in the bore (assuming identical ring placement on the two comparable engines' pistons) and that will allow air/fuel to be trapped there and not burn. I routinely run pistons at .005" above deck, mainly because I want .030-.035" quench distance with the Felpro .039 gaskets. You also want to minimize the chamfer on the top of the bore as this too can work as "dead volume".
On the aluminum option, you have to maintain some distance between the piston and head, but some of the fastest engines I know of just touch at very high rpms. Just enough to leave a mark. The less "dead space" you have in the chamber the more mixture gets burnt completely and more power is realized.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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