asalikus :
Get 500w PSU with a 7950, it's cheaper and more powerful than both.
In what universe is an HD 7950 cheaper than an HD 7870?
HD 7870 - $170 (-$30):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131492
Add $40 for the HD 7950 but get only a 4fps increase.
HD 7950 - $195 (-$15 mail-in-rebate):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150671
Add another $40 and you'll have the GTX 760 but only another 5fps increase:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814500306
Note that these framerates are from BF3. In other games, like Far Cry 3 for instance, the GTX 760 gives you 13fps over the HD 7870. In the end, if you're looking for the best value for your money, you can't beat the HD 7870 at that price level.
BF3:
FC3:
Oh, and excuse me for forgetting, the HD 7870 uses 42W less power than the GTX 760: