How do the cameras compare in terms of ergonomics, mirror slap, etc.

I'm looking for a compactish 645 camera to use with a hanheld. I care about interchangeable backs (no Pentax) but I'm most concerned about slow shutter speeds. Is there a discenerable difference between shooting these two cameras, besides the selection of lenses? I don't care about any auto-features.

The main difference I can see between these two is that the Bronica lenses all leaf shutters and that Mamiya has faster lenses.