I have a fx-4100 and a 7950, fps are at about the 40 range but there is constant stuttering. Settings are all high except shadows which are but on low and the settings for car density, and view distance/quality at 50 or less.
patch it to 1.4 to get the smoothest possible gameplay. its patched up to 1.7 but if you dont have any issues after 1.4 you wont need the later patches unless your gonna play online multiplayer... and even then a lot of the servers only require 1.4