my old trusty 2.67@750 i5 is working just fine with this game...it can easily oc to 4 Ghz. I tried 3.7Ghz but my case needed more air to cool it (Antec Sonata III). Maybe with bigger case and couple of external fans it is easily done....
But in 3 Ghz it easily run this game, so no need to OC now...