Best FPS, hands down, would be a 2600K OC'ed (since that engine actually is, in some instances CPU limited) and a pair of OC'd 580's. If you got that kind of cash, and you really want your setup to last a while without touching it again, 580's and 2600K.
http://www.tweaktown.com/reviews/3784/msi_geforce_gtx_580_1536_mb_in_sli_overclocked/index.html
Otherwise a pair of OC'ed 6970's/6950's and a 2500K will serve you 80% as well as the other setup but you witll save a few $$. 470 is good bang/buck but they can get damn loud during gaming. Like sitting next to a hairdryer.
If money is not a question, go for the best.
If ditching the 2600K for a 2500K means you get more cash to spend on videocards, then do that. The single most important component is the videocards, everything else can get cut with minimum benefits.
So in order of videogame awesomeness and price:
A: Balls to the wall - 2600K, 8GBs of fast ram, 580's in sli. $$$$$
B: Videogame monster - 2500K OC'ed, 8GB of the cheapest 1600Mhz low voltage ram you can find, cheap SLI mobo, and 580's in sli. $$$
C: Performance/$ - 2500K OC'ed, 8GB of okish ram, and 6950's (unlockable) in CFX. $