To be fair DD2 is not good, it works now, don't know what fixed it but this game is not very good.
Screamer/Screamer Rally are much better games than DD2, I have not tested these, all I can say is:
There is no matrox-tool to activate vesa2 compliant behavior on the mystique.

autoexec.bat (vbetsr+vbesetup) do no change anything on chasm and other games.
sdd5.3 (dos/winx) does offer lot's resolutions on chasm but does not help for "stargunner".

Stargunner is in fact really a great game and I would love to play it on vesa 320x240....more tests need to be done.

Stargunner in plain dos with SDD 5.3 detects VESA2.0 but the game is still broken. The additional 40 lines (320x240) have weird colors and seem not to be part of the scrolling-gameplay.