Good build. I overclocked my i7 2500k to 4.5Ghz easily with Corsair H70 cooler. It runs very cool as well. What CPU cooler do you have? You may want to overclock a little bit more because the 2600k is a beast and is hard to defeat.
CF is capped at 200FPS so you won't get much more than that. But with two 6950s, you wouldn't want to play crappy games like CF on that thing. Play crysis 2, metro 2033, batman: arkaham asylum, NFS, Bulletstorm, bad company 2, black ops and so much more I can't even remember.