[Zardokk]

I'd go with an Athlon 64 X2 3800+. The dual cores will really help you a few months down the road when games start utilizing both cores. Also, it's a decent overclocker and right in your budget range. Either that or spend a little more and go for an Opty. They don't have the same stock speeds, but they run on lower vcores, have bigger caches, and are more overclockable.

 

[Zardokk]

The Asus board won't overclock as well as the DFI. DFIs have been shown many times to be some of the best OCers on the market.