One thing you might try is to use the REFERENCE drivers to the Banshee chipset. You can find them at:
http://www.3dfx.com/downloads.htm)
With all the video cards out there, it was impossible to test every single card, so we were told to test on CHIPSETS with reference drivers, not the individual cards themselves.
Video card manufacturers often tweak their drivers to squeeze some extra power out of some of their procedures and to take advantage of assorted improvements, but that often screws with compatibility.