Personally, I wouldn't do it. Even the Q6600 is an old CPU, and it will likely hold back many modern GPUs. A Q6600 will hold back even older GPUs, never mind the latest technology. It will depend on the game, I.e. Fallout is much more CPU intensive, and the Q6600 would not keep up at all. Other applications it might just cope. Overclocking is always on option, but even then you're likely to struggle in many newer games considering the age of the Q6600.
It will be OK in a few applications, but I really wouldn't recommend it, especially not for newer games. Additionally many modern games call for 8GB RAM nowadays too, and this number is increasing.