As it is only for gaming then, I won't say don't get a 2500k, I'm sure you do other things and it would be faster and probably feel in general a touch more responsive, and its easier to have a silent midly overclocked 2500k system than a heavily overclocked Q6700 system, I think you can get an extra 200-300Mhz but power/noise/heat and you'll be fine performance wise.
Honestly, with a quad and a 6950, I don't think you should be in a rush to upgrade for BF3(says the man who just bought a 2500k/mobo and who is a bit peeved my heatsink didn't show up before tomorrow

, only for timing, I use it for a lot of things Sandy will be faster for).
I'd say, hold your cash, wait for new gen gpu's, see what prices are like, and potentially with lowish stock on new cards you'll be ready, money wise, to jump on a 7950 basically on launch day.
Q6700 + 7950 WILL, without question be a better gaming rig than a 6950 with a 2500k. Of course, 7950 + 2500k would be nicer overall
See how a new gpu goes, if you feel you aren't getting the right framerate then think about holding on till Ivy or jumping on a 2500k.