Wo-Nelly

What kinda compression should I run? this would be for a H22 running a sc61 turbo and a built block. This is not all done of course, but I just want to have a game plan. I'd want to make 500whp if it's possible so I'll boost as much as the turbo can support. I'm thinking maybe like 9:1? Or would lower be better? That leads intot he second question, I'm wondering which would be better, high (10:1) compression pistons with a thicker head gasket to lower compression. Or a lower compression piston (8.5:1) with a thinner gasket to raise the compression? Is there a difference?
Thanks