I've been reading the MURC forum and I get the impression that UT2003 was one of the most popular games for Parhelia. It's likely Matrox paid special attention to the game (and Unreal Engine 2 in general). Some of the MURC people also played this in triple monitor mode.

When I played it on Parhelia, it seemed to run quite nicely. I didn't notice any visual issues. However, it seemed to have an occasional stutter as I ran around, which didn't fit with the rather high framerate. Still it did run quite acceptably.

Overall my impression of Parhelia is that, for gaming, the drivers are likely most optimized for Unreal Engine 2 and Quake3-based games. These were prevalent at the time.

Do you by chance have a Matrox P750 or P650 AGP to test? Unfortunately, the P750 is a bit uncommon.

Nope sorry. Parhelia is the newest Matrox card that I have.