One thing that people dont seem to understand is that a Q6600 and a new high end GPU is not a good combo in any situation. Newer games and newer hardware is aimed at newer CPU architecture. No matter how high you can overclock a Q6600 or Q6700, it will still bottleneck a high end GPU in some cases. I guarantee anyone using one of these CPUs who think they have reached the point of "no bottlenecking", when you do eventually get a new CPU you will see significant FPS increase.
There is no NEED to upgrade a Q6600 right now, but if you want more performance it's a must.
Q6600 = Phenom II performance, so if you can overclock a half decent amount it will do ok.