G100A isn't at least.

Mystique (MGA-1064SG), Mystique 220 (MGA-1164SG) and probably Millenium II (MGA-2164W).

Cool, Millenium II looks like an option as well.
4MB versions of the Mystique and Millenium II go for about the same price, Apart from the slightly faster performance of the Mystique is their any benefit of one or the other?

This will be going in my "experimentation rig" a Duel PPro that I want to try out OS2, NT3.5, and naturally Games that support MSI

AFAIR Millennium II isn't always compatible, some games look for specific strings in the BIOS or wherever and do not recognize it as a Mystique card. The card is otherwise fully compatible with MSI, I'm thinking you could bypass this with some BIOS modifications.

Matrox Mystique
(IS-MGA-1064SG-D) - best compatibility
Matrox Mystique 220
(IS-MGA-1064SG-G)
(IS-MGA-1064SG-H)
(IS-MGA-1164SG-A)