ASUS 9980 Ultra slowdown solved
We've bought 5 ASUS 9980 Ultra cards for our linux image generator project.
What we've got was that only one of them worked with hardware 3D acceleration, while others were very slow even in KDE.
To make long story short the problem is that there are old ASUS 9980 which work good and new ones which are terribly slow under Linux.
So solution which worked for us:
flashed them with NVFLASH utility and LEADTEK BIOS (A380U.ROM) from DOS boot diskette