well I dont think its shaders that are slowing your down (UT2k3 uses shaders to mean something different that DX8/9 Shaders for maps/textuers). That smoke is made with a particle emitter and that will slow down about anyone.
However part of the issue MAY be all of the custom static meshs that they use. Each one has to use a non standard collision hull. I have an issue with my mod were you try to spray paint (ala the spray paints from HL) on one of the walls here and it wraps the spray all over one part of the "wall" (which is really a static mesh as the actual BSP wall is behind it). I have not been able to find out why this happens as most other maps it does not happen. So right now my spray paints in Icetomb is broke
I looked at Icetomb in the editor a few weeks ago and nothing jumped out as being wrong so I think its an issue with how I set up my projector...anyways I can try to look at it again tongiht and see what else it has to make it "harder" than the other maps.