Check out toms hardware reviews. Normally they do comparisions of new products. If I was you I'd be researching which series overclocks the best. As long as the cache is the same its irrelevent what speed the cpu is. Because you can overclock them about the same. Give or take a few hundred mhz. Not sure about the new series i'd just spend $300 and get the q6600 quad core
You'll be set then.
Any of those mentioned shouldn't bottleneck a 7950gt. You planning to run XP otherwise don't waste your money on that get a 8 series card.