Hi,
about the B revision from this chip, i did not find any information.
Just beginning from the MGA-1064SG-D one there can be found infos.
It was produced since calender week 31 in year 1996.
The B chip seems to have been just a short time before, because it was quickly switched to the D revision.
Does it have any bugs or was it not intended for the release product?
If anyone has informations please let me know.
And what is the production date of your Matrox Mystique video cards?

The date can be read in the second line from the chip.
Examples:
9637 = 1996 in calender week 37
9707 = 1997 in calender week 7

I got the clock speeds from the internet and should be viewed with caution:

Matrox Mystique 170:
- MGA-1064SG-B ? / ?
- MGA-1064SG-D 50 MHz / 75 MHz or 55 MHz / 82,5 MHz

Matrox Mystique 220:
- MGA-1064SG-G 60 MHz / 90 MHz
- MGA-1064SG-H 60 MHz / 90 MHz
- MGA-1164SG-A 60 MHz / 90 MHz or 66 MHz / 99 MHz