The fourth core will help with general system performance, NOT anything to do with in-game performance. for example, with the 4th core you could run other applications(like recording gameplay via FRAPS or similar, Virus scan, etc.) and it wouldn't affect the FPS within a game you are playing at the same time. But games themselves do not utilize more than 2 cores(at least not yet). Where you get the bottle neck is if you have an older and slower CPU and it is unable to supply data fast enough to the GPU. To test if this is the case, reduce your video settings to lower detail. If your FPS increases, then the GPU is your bottle neck, if your FPS stays the same, then your CPU is the bottle neck.