[wblynch]

... The Mamiya with its left hand grip requires right hand focusing, which is certainly okay, but it doesn't feel as natural...

...One disadvantage of both cameras is the lack of removable backs. All too often I have a half used roll of film in the Mamiya and wish it had a different film in it for what I want to shoot..

The first statement is why I threw the grip for my M645 away. It actually feels good in my hands in it's trimmed down state.

The second statement is easy to solve... get TWO bodies! (they're mighty cheap now compared to the 'olden days')