I found this while i was on the www.planetunreal.com website, gave some sort of insight as to what rig you might need to run UT3.
"Your Crappy 2½ Year Old Computer Will Run UT3 - RaptoR -
7/31/07 7:18 PST - General UT3 News
Unreal Tournament 3 lead designer Steve Polge dropped by the BU forums to talk about the recent glut of UT3 footage to come out of Comic-Con. Steve comments that the top-of-the-range Alienware systems used at Comic-Con would easily run UT3 at max details, and that UT3 playtesting was being done on 2.5 year old rigs with mid-range GeForce 7800 graphics cards.
A few comments: we're still working on player and pickup visibility - we're confident we've got a system that will address those issues well. We haven't fully implemented this system because we need to make sure all character skins and level lighting is finalized before we tweak it. We also have a very nice material based system for making it easy to pick out team colors on players and vehicles at any distance, where the red or blue is boosted based on distance. That way you get natural looking characters and vehicles up close, whose team is clearly distinguishable even at the furthest viewable distance.
Those machines are way overkill for the highest detail level - the only reason it wasn't turned on was because the option isn't exposed in the menus. We do all of our play testing on 2.5 year old systems with 7800s in them - that's our target medium detail (what you were seeing today) platform. Quad core doesn't help much for performance, but having a dual core machine is a big benefit.
Stinger primary fire is still a hitscan minigun, although that build has some issues with the tracers feeling a touch laggy. Stinger alt-fire is not hitscan, however."
hope it helps somewhat