Your rig is vastly better than mine and only had a very small jitter in one or two SP spots, none in MP. I ran at max settings on 16x10 resolution. Something must be off if you are getting noticeable low fps, 60 you will not see any slow down.
Holding at 40 fps should get you a smooth gaming experience, not sure what you mean by keeping up, you won't notice a difference if its 40 or 140 fps. I ran that game max on a FX-60 @2.8 and 3870 at 1680x1050 smooth (no AA didn't need to), still thinking something is a miss here. Unless its just that your server cpu just doesn't like to game then sell it and buy a 930 or something. Could at least give overclocking a try first.