Humus has found a tweak that can boost your Doom3 performance by 40% on ATI hardware.

I picked up Doom3 today and let be begin by saying it's a kickass game so far. A few minuses like weapon reload (which I find add nothing to a game, except annoyance, so I don't know why many devs keep adding it to their games), but overall much above my expectations. Anyway, to the fun part, exploring the technology. I think I've found the source of why this game runs comparably slow on ATI hardware vs. nVidia at the moment, and found a solution to the problem.

How to Boost your Doom3 Performance by 40% on ATI Hardware

Thanks to EliteBastards.com