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.

I am back on that machine for a nice multi boot setup. For those of you who have a machine with a mystique inside. What win95 driver are you using? I just figured out, that the driver I recommended (the very very late/last one from 1999) does not install, if I am using win95a, seems that it requires win95b, so I have to use a different driver.

UPDATES:
Stock 370 driver from the mga-cd has no working v-sync in ddraw as expected. if you want to try it (DX5 required) https://www.pouet.net/prod.php?which=8410
I have not tested the next two drivers, but I did that long ago and the only working driver was the very latest with files from 1999. Installing this driver over version 370 always crashes win95a on startup after reboot.

So in short. Either a third party tool that fixes vsync on ddraw on early drivers, or changing the OS to win95B and using the very latest driver.

Edit2:
Power-Strip and MGA-Tweak do not offer v-sync option. Beside some scene stuff, also JazzJackRabbit2 is affected, so...I am going back to the already fully tested and working setup. Win95b with the latest driver.