b16 block and GSR head? Why change pistons? What CR are you shooting for? The smaller combustion chamber of the GSR head should bring it up about half a point or so. Why not use the compression ratio calculator on cspeedracing.com?

If I were you, I'd keep stock internals and perhaps a Skunk2 intake manifold. With what you've got, you'll be pretty content the power it'll put out on OEM parts.