that is socket 775 so the c2q 6700 should be ok . you would need to be sure that the cpu and motherboard are ok with the same ram though. they both have specs for the ram they can work with. my c2q 6600 uses ddr2 6400.
so happens that i just looked up the cards that would compliment the cpu you already have. there is a new nvidia line , it is the 750ti and low and behold, the thing is dropped down considerably. they are normally around 150 usd. it is almost as nice as the gtx 660 and way better than a 6750 or r7 250. these 750ti cards are the low power sort so your existing power supply would probably be just fine
if amd is your preference, there is a few r7 260x cards that have dropped considerably in price also..
Edited by synergy513, 27 June 2014 - 03:41 PM.