Why do you guys think CPU and GPU will clash at all.
I have been using ATI 5770 + a dual core cpu for a long time running games at max settings with 4x MSAA without any problems.
Infact I am into game development and from my knowledge, with a good GPU supporting shader model 5+ (which only the latest releases are using anyway) you can always get good performance because the fill rate + Shader processing is bound fully to the GPU and games are not entirely CPU bound.
If you get NVdia, you get PhysX which also solves the issue of Physics processing in the CPU.. so I dont see any problem with an old CPU. The cpu you mentioned has SSE 3 I reckon and even the most recent games are not written for (above) SSE 3 (although that will change). So vector processing in the ALU will not improve if you get a better processor as no programs will use it.
All developers build their program with compatibility in their mind and the do not push boundaries abruptly.
It will change however.
So, I recommend you get a performance graphics card like ATI HD 6800+. It will be more future proof.