I'm surprised no one has considered the 6950 as the culprit to the problems the OP is having....
No one seems to have taken into account that 1GB of vRAM @ 1080 & Ultra settings in the games he says he plays is not enough to maintain a solid 30+FPS without using his DDR2 system RAM as an offloading point. (for the purpose of this post I'll assume hes using a 22"+ monitor of some class/resolution)
Yes, the i5 upgrade will yield very nice improvements for the most part.... BUT, if the 6950 is indeed the problem it will only go so far to curing the issue and a new graphics card would be a much better investment at this point.... certainly so seeing as the Q6600 (at the OC mentioned) still does a very sound job in the gaming arena and I doubt is much of a "bottle neck" to any game out there currently... most of the titles on the market at the moment are console ports that utilize very little CPU power or graphical power, any way.
Maybe you regulars should give that some thought before you convince this guy he needs to spend 3x the amount and still have 25fps due to a poor amount of vRAM.
What resolution are you running at?
Is the 6GB of RAM you listed running dual channel (2x2GB+2x1GB) or single channel (2x2GB+2GB)?