1280x1024, 24-bit color.
UT2k3 (the full game, not the demo) averages around 60fps or so. It gets down to 10-20 at times, but only if there are a ton of bots in a large room.
The only thing I can think of to increase performance would be enabling SBA and/or fast writes (but these options may decrease reliability -- they worked for me, but they don't work for everyone, which is why they're disabled by default
First of all, look in /proc/driver/nvidia/agp/host-bridge and /proc/driver/nvidia/agp/card to see which of SBA and FW your AGP bus and card are reporting that they support. If both files report something as supported, you can add an options line to /etc/modules.conf (options nvidia NVreg_EnableAGPFW=1
or options nvidia NVreg_EnableAGPSBA=1
or options nvidia NVreg_EnableAGPSBA=1 NVreg_EnableAGPFW=1
if they both support both), then either reboot, or exit X and rmmod the module, then restart X.
If you have a Via chipset motherboard, you're probably running at 2x AGP, as well (there have been reports of very wrong AGP drive strengths or something with AGP 4x on some old Via mainboards). I'm pretty sure you can pass NVreg_EnableVia4x=1 to get the drivers to enable 4xAGP. You probably won't notice a difference there, though, at least not in glxgears. Maybe in UT2k3, but only if it uses more texture memory than your card has onboard.
As for stuff to add to the config file, I don't know of anything.