I just upgraded my nVidia 8600 GT to a ATI Radeon HD4890.
My in game graphics are now substantially better as you would assume.
However the maps now take a lot longer time to load, averaging about 40 seconds.
Also, when opening up the game I often get a black screen for a long time.
My loading times were much faster with my previous card. I have researched this a little and I think I've found that other people have had the same problem.
Ive also heard ATI closes any threads opened on their forums about this issue.
So yea, I'm really frustrated because I compromised to buy this card. I didn't want to wait for a GTX 275. Even though they perform pretty much the same on the charts I wish I stuck with nvidia and i wouldnt have this problem
No problems here, I had dual 4870 X2s and now three 4890s and I do not have any problems with CoD:WaW, I play it every week.
It might be conflicting drivers, download driver sweeper and new drivers for the graphics and motherboard. Uninstall your current drivers (motherboard too) and reboot into safe mode, once there run driver sweeper and clean out any remaining drivers files for graphics (nvidia then ATI) and the motherboard. Now install the new drivers starting with the motherboard.