570 is about equal to 660 (non Ti). or 7850 from the red team. for 125 there is no current gen card can compete with 570 performance. going from 8600 to 570 will very huge performance improvement. for sure you need to double check your psu as well since 570 will consume more than twice or even triple the power compared to your 8600.
So there is not any reason to buy a 660 or 7850?