And incidentally I've had no issues shooting the pro or AFD at 1/30 or so. Let's see... this one was at 1/20 in low light with the afd handheld.
These are great handheld cameras. The best of the 645 bunch for ergonomics is probably the pentax 645 nii, especially if you like shooting vertical format, but I like the ability to swap backs on the mamiya 645 pro and the modularity of it is great. You can go with it as a little box with waist level or slap on a finder and grip and have something like a heavyish 35mm body. The overall price for kit and lenses is also outstanding for the mamiyas and the bronnies too.
The Mamiya 80/1.9 is especially fun for 645 but let's be clear that it's not the standout in the mamiya 645 line, it's just a fun lens for b&w, especially portrait stuff. If you want super performance the more modern manual 80/2.8 is the way to go.
My best advice is to get these cameras in your hands and see for yourself.