8GB for gaming?? You're out of your fucking mind. The rest of your rig will be obsolete before you outgrow 4GB. In fact, if you've got enough money to blow on 8GB of RAM, chances are you'll be upgrading again before you outgrow 2GB.
Seriously, buy it when you need it. It'll be faster, and it'll be cheaper. Trying to futureproof a gaming machine is little different from flushing money down the toilet.
so true. Use the money from the over kill 6gb and buy a better video card or something.