January is end-of-line for the 8800 series cards. That probably means a new high-end card from nVidia in January or February.
Sometime early in 2008, ATI is bringing out a dual RV670 (HD3870 x2) card that will have a memory bandwidth of 115.2 GB/s.
Compare that to the memory bandwidth of 103.7 GB/s for the 8800 Ultra and 86.4 for the 8800 GTX.
Sometime early in 2008, nVidia will counter that with a dual G92 (8800 GT x2) video card.
Some people on this forum think the X1900XT is a high-end card.
The next generation Mac Pro will not have a video card that can touch your 8800 Ultra.
One year later and the 8800 Ultra and 8800 GTX are still king of the video cards.