Well, since UnrealTournament is essentially the Unreal engine with enhancements, it was originally developed for Glide and software modes alone.
Direct3D was added later (and even then was originally for DX6) as a bolt-on to the original software.
So, the end result is that your performance with D3D is partially based on which version of the API renderer patch you happen to be using.
Also, you'll find that the end results with DX7 vs DX8 varies in certain hardware cases. The majority of people will find an improvement with DX8, but some will actually come across a decrease in performance.
Your best bet to list your hardware and operating system specifics and hope that people with a similiar setup let you in on their experiences.