I have a Q8200 and a 6870, my GPU is only being used 70%.
I can play on a mixture of high and ultra on my TV with a resolution of 1368x768 and it's super smooth. I'm guessing around 50-60.
With a 2600K I'm guessing you could run it pretty well on a 1920x1080 or something similar. I'm not sure what else you use your computer for but a 2500K and a pair of 6870's or a 570 would be better.
And before anyone tells me my computer is wasted on that resolution, I'm planning to move it back to my monitor soon.