I have the same gosh darn problem,my game is stuttering like ****.This game worked fine until patch 1.4 ,*** those idiots did to the game?
My pc is not the problem:
HD 4890 1GB
AMD athlon II X3 455 3.30 GHz
4gb ram (not so much but still this game is ****ed up)
I even reinstalled the windows(not just for this game) but the stuttering is still there and the the difference betwen very low graphics and very high is null.
My fps goes like 60-15-60-15 etc .I had the same problem in patch 1.3.5 but then they patched up the game and it worked fine,now **** me if they know what are they doing to this game.