They both are pretty much the same price, will be mainly be playing BF3 multiplayer, maybe some CoD, or Crysis 3 (not likely), and some strategy games, like Company of Heroes, or Shogun 2. Also I won't be upgrading for 3-4 years, so longevity is also an important factor.
There is only a small difference in performance between the 7950 and the 7870 XT . If you overclock the XT it might perform as well or better than a stock clock 7950
Of those two the intel/7870XT is the better choice . But it wont perform better in demanding games like BF3 or Crysis 3 , but it probably will in older games
Make sure the RAM you are using is rated 1.5 volt or less
And consider building using the Fx 6300 and the 7870XT so you can afford a bigger monitor . A 24 inch screen really doea make a difference
If I get, the fx6300, will there be a huge difference a 3-4 years down the road? And as for the monitor, I'll get something at microcenter. And will I need the hyper 212 evo cooler, to increase longevity?