I like your suggestions. A little research shows the Mamiya and competitor Bronica look like good contenders. I like using fill flash so I might glance at the etrs (?) for a bit. I spent all my time researching 6x6 and larger cameras because that is what I found in flea markets. Some KEH models of the Bronicas are in my price range so far!
I also like how modular they are, offering a slow bargain hunting method for build up.
SIX batteries! The functionality of the pentax looks nice, but its a bit of a brick with all the batteries and that handle you cant remove.