Dude, if it was limited at all by fillrate, memory bandwidth, or texture rate, then changing the resolution would have a significant impact on framerate. It doesn't. So it's most likely limited by the CPU.
Anyway, I know that on my system, UT2004 is one of the few games I play in which I can run at 1600x1200 with 8xS and 16-degree AF at high framerates (7800GT SLI), with all in-game options turned up to the max. I mean, if I can run that high, this game has very, very little fillrate limitation compared to most modern games.
