Maskedgeek, let me be the one to show you a test I made long time ago with very basic equipment, and if I think back not realy quite accurate, but it can still give you a ballpark of the difference between two exactly the same blocks 6mm AL spiral and 6mm Cu spiral , it is around 5°C with that testing Duron, and if I would test with something hotter like overvolted Axp the difference would be even greater here:
http://forums.procooling.com/vbb/sho...&threadid=2183