Go with what the manufacturer recommends for the piston and you'll be fine. It's all about how well the piston dissipates heat, how high the top ring land is and how much the piston will expand.
There again it is a little confusing; the sheet that came with the pistons says follow the ring manufacturer's suggestions; the Ross sheet that came with the rings (which are in a Total Seal box with a Ross part number sticker) gives the .004"/inch for top ring and (I think) .005"/inch for second ring.
I said Sealed Power before but they are Total Seal rings.
