If your games are cpu dependent, like BF3 multiplayer, then buy the stronger cpu, the 3570K.
If you play BF3 single player, and most other games, the better 7950 card will be better.
But, really, the 7950 is not very much stronger than the 7870.
My take is to go the 3570K route.
That leaves open the option to upgrade to a much stronger amd 8xxx or nvidia GTX7xx card next year.
Do not plan on cf/sli unless you anticipate triple monitor gaming.
If you go the fx 6300 route, it is much harder to upgrade to a stronger intel cpu and motherboard. Such a change may also require a windows reinstall.