SantaDuck created a nice little benchmark package (29.1 KB) to let you know how badly you need to upgrade your videocard. Basically just download the files to your main UT2004 folder, select the screen resolution and double click. Very easy.
The CTF map was selected because it resulted in the most active action out of any of the maps. Most of the other maps were very large and task-oriented, which means the benchmark would just watch a bot sitting by itself shooting a gun installation, or idly standing and building something, or worse just running alone across a large map. I could make other benchmarks, but realistically they would just suck as a measurement of your rig.