Thinnest head gaskets for a magnum?

Going from .050 to .027" thickness drops the volume by about 4 cc's which is good for about .3-.4 point in static and dynamic CR. You'll feel the difference.

With thin head gaskets, I'd suggest having the heads checked for flatness and a skim cut taken at least ...it won't take much to have a gasket leak. People ignore this far too often IMHO.