There are 2 main differences:
1) You can attach Cybervision to CSMKIII = fast RTG card with 3D
That would be the CyberstormPPC and CybervisionPPC. The model previous to that was a Zorro2/3 card that featured a fairly primitive S3 Virge gpu. So far as I'm aware, you cannot attach at CybervisionPPC to anything other than the CyberstormPPC.
SCSI... Good luck finding 4Gb SCSI hard drives these days. You'd be better off investing in a fastATA controller and getting a 4Gb CF card.
--edit--
Was having a wander around the interwebs and found this, thought you might be interested:
For sale (you'll have to contact them beforehand regarding availability I suspect)
Cyberstorm MkiiiCyberstormPPC