G5's and Copperheads are both great gaming mice. go to a local store and feel them both as they both feel differently, you'll want to pick the one you like the feel of most. I personally liked the copperhead more, but I know a number of people who prefer the G5's feel.
(i use a razer diamondback btw, but I may get a copperhead to replace it for gaming and use the diamondback more casually soon)