Doom 3 Question

[XboxodX]

I have a Radeon X1900XT. When I pay Doom 3 At 1280 x 1024 @ ultra high it is very laggy, but if I back it down to 800 x 600, it isn't laggy anymore. It can't be the computer, because I can play Prey at 1280 x 1024 @ ultra high and it isn't laggy. What gives?

 

[BBA]

I had the same problems, then I went to the cat 6.3 driver with control panel and all is smooth as glass now.

The newer cats (6.4 and up) all seem to suffer this performance problem on my system.
You can get this driver from ATi by getting the older drivers page for the fire mv card.