I wonder if the different revisions will reveal why some games apparently don't work on the later HiSaturn model etc.
Because VA10 and later Saturns have the SCSP and 68k integrated into a single Yamaha ASIC, and a few games trip up those 68k commands that this ASIC does not support. Exact same bug as why the Genesis 3 can't run Gargoyles.
One of the Sega tech bulletins mention which two commands are not supported.
As far as I know, there are only two games with such a problem: Space Harrier, and Outrun. Both of them got second revisions which fixed the issue. (and no, Metal Slug is NOT affected, unlike what rumors and Wikipedia state)
But, Model 2 HiSaturn is identical to the late 1996 PAL models - same VA9 board. So maybe you are talking about some other problem?