Q6600 is actually "overkill" for CS GO.
Unless you have some compatibility problems it will do the job.
That CPU (I had it for many years) was good in everything I played except:
Starcraft 2, physx calculations.
In everything else the GPU was the limiting factor.
I am using today a laptop with a i7-2760 and its barely faster than then Q6600 (due to hyper threading) allowing me to stream and play CPU intensive games with some stutter.
With non CPU intensive games I can Stream AND play with high FPS no problem.
So, if its budget you are looking at, (especially if you already have the motherboard and the ram for the Q6600) its a decent option.
However, if you DONT have the motherboard and ram, there are good options out there in...