Here is one simple .ini tweak that can completely change the way your UT3 looks.
It removes the red hit effects, tunnel vision, desaturation, depth of field (distance blur), blue toning and colour post-processing. And generally makes it a lot more simpler, crisper and cleaner - more akin to UT2k4 (but with all the benefits of highly detailed textures and models of UT3).
Open - /my documents/my games/unreal tournament 3/utgame/config/utengine.ini
Under [Engine.GameEngine], replace:
DefaultPostProcessName = FX_HitEffects.UTPostProcess
with:
DefaultPostProcessName = EngineMaterials.DefaultThumbnailPostProcess
And that's it.
I have actually added the new line underneath it and put a ; before the original to disable it, and switch between modes when taking screenshots/testing maps. But in general play, I always use the ThumbnailPostProcess.
VCTF-SuspenseBefore

After
DM-DeckBefore

After

As this basically disables the 'scene effect' which is a setting inside each map. The effects can vary from map to map, depending how much post-processing the mapper had done (but in most cases, it looks better).
I prefer this method of tweaking as you can set the in-game settings all to max (or default) and then this setting will sort out the rest. Minimal effort, maximum result.
And if your thinking
'will this make the game perform better?'. Well I can't be sure of that, although it does disable some effects that would otherwise take some CPU cycles to render, so might help, but you probably won't notice any difference in fps.