I'm having the odd stutter watching live tv and when recording and I have found that the problem is directly related to the hard drive in my case.
Perhaps its worth looking at have a 2nd hard drive dedicated to your windows swap file or for MP. Or at worst case replace the HD with a superior quality drive.
Also in my case if I try to use exclusive DirectX mode MP will not work, it doesnt actually display anything on the screen, not even the front menu |