Its was/is a problem with UT2004 running on 8-series cards on WinXP (Vista drivers did not have this issue, and since you mention running DX10 you are probably on Vista, and would not have been effected), and it has gone unadressed for more than a year untill now.
Though i'm sad to say the issue is not entirely fixed, on certain maps, i still get micro stutters, its not nearly as bad as it used to be, infact the stutters are so brief they don't even register on the in-game FPS counter anymore, buy you can feel them, there's still some of it left.. but it is only on some maps, not all like it used to be.