It really depends on the game you're playing. Not many games are CPU-bottlenecked, with SC2 and Civ 5 really being the exceptions. Although, I know somebody with an "old" high-end gaming rig with a Core 2 Quad Q6400 and he has no problems with either game. Realistically you might not notice much of a difference.
I don't have either so I can't speak from experience, sorry.