A fast CPU like the E8400 will not bottleneck a Single GPU anytime soon. It's when you go multi-GPU that the CPU will start falling behind.
If you only have a single card (the wisest decision in my opinion), the E8400 will not bottleneck any GPU.
Plus, let's say that in 2 years or so, the E8400 will start bottlenecking the fastest GPUs around at that time; you just bump that beast to 4ghz and there u go, no bottlenecks again for a long time.
The E8400 and all the other high-end Duals will last a good while for games, I believe. They're pretty powerfull little beasts.