Firstly those are hardly 'early' Matrox cards - Matrox had been making S-100, ISA and VLB cards for years before this. These are decidedly mid-period Matrox cards.
Secondly, how big the differences are depend a lot on what you want to use them for.
A) Matrox cards are mainly Windows accelerators, so DOS performance is going to be mainly dependent on memory fill rate, which is usually bottlenecked by the (PCI) bus. Expect near-identical performance there, as reported here
B) In Windows the 2D performance is strongly tied to core/RAM clocks as can be found here; Matrox cards were very fast at accelerated 2D desktop stuff.
C) 3D wasn't the cards' strong point. Performance was actually pretty good (see a lot of benches here), beating contemporary S3 and ATi competition in most benches - but features (fogging, filtering, blending, sometimes basic transparency and textures...) were lacking resulting in very poor visuals. Supposedly the Millennium II and Mystique 220 (MGA-1164) should be better, but still not up to par, even the low 1997 par.
D) analog image quality was and remains Matrox' strongest point. These cards had high-quality and (other than on the Mystique) high-end RAMDACs enabling high resolution and refresh rate settings and excellent analog filters and components to ensure crisp picture quality even at the highest supported resolutions and refresh rates. The hard specs were determined by the RAMDAC (see list from B again), and I can't find a modern RAMDAC clock to supported resolution/refresh table (if you can edit old .xls sheets, this one will do the job: http://www.cs.unc.edu/Research/ootf/FAQs/Video/GTF_V1R1.xls ), but bottom line the last Millennium I and Mil II with their 250MHz RAMDACs were vastly superior to the rest in this list and just about anything else in the PC market at the time, alllowing 1280x1024x24b@85Hz - and having the circuitry to do that without blurring, at least if your monitor and VGA cable were up to it. The worst of the lot would be the first Mystique, which had a 170MHz RAMDAC and so could manage max 1024x768x24b@85Hz - which was still better than what an average 1996 monitor could handle. By comparison, a 1996 S3 Virge had a 135MHz RAMDAC which could only handle 67Hz at the same resolution and colour depth, or 80Hz if you dropped to 16b colour - and then you just had to hope the card had good analog circuitry, which was rarely the case with generic S3-based ones. Later Virge/DX and /GX chips, and the ATi 3D Rage II integrated a 170MHz RAMDAC, equaling the Mystique.
