Things seem to have improved considerably with Unreal Tournament under CXG 10.3 on Mac OS X. My observations:
1) On newer gfx hardware (e.g. the GeForce 320M on my 2010 11.6" MacBook Air (10.6.8)) the game runs perfectly well under DirectX with DirectX 9 installed in the bottle; the game won't work well on video settings beyond the standard defaults otherwise. The game also runs well using the enhanced DX9 renderer available here. The unofficial 451b patch available at utpg also works as well.
2) On older gfx hardware (e.g. GMA 950 on my mid-2006 MacBook (10.6.8)) the game won't run using the DirectX renderer, either with or without DX9 and the enhanced DX9 renderer installed; it will only run using the experimental OpenGL renderer. The game does run well using the enhanced OpenGL renderer also available here.
Under both circumstances, the mouse lag issues I observed when playing under CXG 8.x seem to be gone.
tl;dr version - on older hardware like MacBooks using the GMA 950, use the OpenGL renderer with Chris Donhal's enhanced OpenGL renderer on the site linked above; on newer hardware, installing DirectX 9 and using the Donhal's enhanced DX9 renderer (also linked above) is recommended. I haven't had the chance to test this on other newer hardware gfx configs, so caveat emptor.