If you already have the I5/I7/etc makes sense to use them - but if you don't, consider you can mine with a GTX 750ti at ballpark 240h/s using HALF the electric for ballpark $100 *NEW* cost.
That 7950 is going to eat a LOT of electric, you won't see 2 month ROI on it. 4 perhaps - which would still be better than paying too much for a high-end CPU to mine on.
Exactly... if I would have had to pay the full $400 for my 6800k, there's no way I would have used it to build my first mining rig. VERY long road to ROI that cost, even if it does end up pulling the 500-600 M/h that I am hoping for.
As soon as I get my rig up and running, I will report back here as to what HR that CPU is getting.