Keep in mind that I merely ran through a game or two and watched Fraps here and there, but here's my findings. This was with the beta, by the way. I'm not sure how it would apply to the retail game.
The game ran relatively fine for me, considering the dual core and non-Hyper-threaded CPU. I saw the 50FPS-60FPS+ range, and often enough even. However, it goes without saying that along with that, I also saw drops to ~30FP, plus or minus some, and I surely blame the CPU more than the GPU.
It didn't really drop below 30FPS too much (I was playing the smaller of the two maps though, I'd expect dropping more into the 20s range with heavier gameplay), but even if that might sound good, it was way too inconsistent, which ruined it. You want a CPU that can pull it's worth and keep the minimum frame rates up here.
I'd say it might be okay if you just want a run through single player, and maybe it'd be better if you could cap the frame rate and live with a 30FPS constant (if that), but I'd say your typical 4GHz Core 2 Duo E8x00 is a realistic minimum for this game, speaking from a more pronounced enthusiast point of view. More casual gamers would be more fine with it, I suppose.
Originally Posted by Mike-IRL
I played the beta well enough with my i3 at 2.8GHz, not as well as when it's overclocked but I think an overclocked e8*00 should have no problems playing it.
Hyper-threading is probably going a long way in making a difference there compared to the strict dual core Core 2 Duos.