With all the discussion lately about how Half-Life 2 will run on ATI hardware compared with NVIDIA accelerators, BonusWeb.cz emailed id Software's John Carmack to ask how DOOM 3 and other games are likely to be impacted by the difference between the two graphics platforms running DirectX 9. Here's how he responded:
Unfortunately, it will probably be representative of most DX9 games. Doom has a custom back end that uses the lower precisions on the GF-FX, but when you run it with standard fragment programs just like ATI, it is a lot slower. The precision doesn't really matter to Doom, but that won't be a reasonable option in future games designed around DX9 level hardware as a minimum spec.