Tundra got it.
The 3570 is enough for any existing video card (except the dual-GPU monsters), if youre playing in, or above full-HD. The i7 would only be an advantage in very small resolutions - but hell, you dont want to play in 600*800, do you?
As for the 7870: its nearly equal to the gtx 580 and the old 6970, also only 15% faster than the 3 years old 5870, what you can get for like 100$... i doubt that many could notice the difference withouth fraps.
(my secret favourite, a 5870 CF from 200-220$ and the 7970s can run for their money

)