Since depth of field is a condition of focal length of a lens and not of format, you should have an accurate idea of what the depth of field on a 100 mm Bronica lens will be based on your earlier experience.
I have a Bronica ETRS and when I used it frequently I would normally use a 150mm lens for portraiture. That lens would be roughly equivalent to a 70 mm focal length lens on 35mm. Still slightly wider then the usually accepted 85 to 105 mm lens that many 35 mm photographers use for portraiture. Hope this helps in your considerations. Good luck.