rb20 head gasket?

[squbafreak15]

so now that ive got my head off imgona replace the head gasket thats on there. (its some sort of metal) i was thinking of doing a cometic head gasket. but idk which to get they offer two diffrent metals mls 0.040" and then mls 0.051" they also have many diffrent thicknesses. i was kinda thinking of putting a thicker one on there? to lower the compression so that i dont have to run as much boost to get power? is that a bad call and the stock bore on the rb20 is 80.0 right