$650 Gaming Build-Need Help

So, basically, I've decided on an HD 7850 because it can max any game out right now at 1920x1080, and 2GB of GDDR5 should make it relatively future proof. I'm getting 8GB of RAM for future proof reasons ($20 more than 4GB). I'm getting some cheap ASRock mobo, a 500W cooler master PSU. a Zalman case (Z9) with 4 120mm fans already in it. And last, but not least, my CPU. I've been tossing around a few ideas, and here they are. Phenom II X4 965 BE, and OC it a few hundred MHz (to around 4.0GHz), an i3 sandy-bridge, or just a sandy bridge pentium, and when I have the money, get like a 4th generation i5. what do you guys recommend? how does an OC'd Phenom II X4 stand up to the almighty sandy bridge i5/i7? an i5 is out of the picture at the moment, and going with the future proof theme, I would really like a quad-core for when more games start utilizing the four cores.