I don't know what SmartGart was then but now that I reinstalled DX 8.1 and Cat 2.5, AGP Speed is 4X and Fast Write is on. I assume it was probably the same before, although I really don't remember. The two games that I really had problems with were Return to Castle Wolfenstein and SOF II. The game menu for both games would freeze for 4 or 5 seconds and the my mouse pointer would be free for half second. I finally got RTCW started and it ran for a while and then froze up. Menu was the same for SOF II, but the game ran very choppy even with all the video options set very low. Before the upgrades, (and now), I ran all video settings at max and resolution at 1280 x 1024 and everything ran fine.
I've seen on other forums, people with the very same problem.