This is my best guess whats going on...
I think they briefly mentioned making a change (in these new versions) to the turning rate? I really believe that is what is the problem. I think it was intended to make multiplayer more fare (good intention), but in the process we are experiencing this stuttery jerkiness.
I really only notice it when on horse back making a turn and independently turning the character at a tighter turn (especially in first person, with a bow....you really see the hand holding the bow jerking as the turn is made, as if it now has to pause at certain intervals). In the older version this kind of turning and shooting would have been completely smooth.
I've tried every combination with the graphics settings and DirectX...there is a higher frame rate in DX7 but I still can see the stutter. I hope that if I'm correct, that the problem is with the 'balancing' that has been done to the turning rate, that they would please consider reversing that back. I will probably play from time to time even if they don't, but I don't love the game like I use to...very sad.