In my case I would need movements - just as much as I do with LF. And superwide lenses too. So a 6x17 back for a 4x5" camera is not a viable option: I want a 6x17 rollfilm holder for a 5x7" camera so I can use a 75mm lens with a little movements.

Until a reasonably-priced one comes along, I'll stick to 6x12 in a 4x5" camera (and a 47mm lens), or cut a 30cm piece off a 120 film and marmalade it to the glass plate in my 24x30cm camera and use a 140mm lens.