So I'm currently shooting with the older Pentax 645, but am thinking about switching to a Mamiya 645AF, mainly because of the backs. 1) I'd rather be able to switch mid-roll, 2) The Pentax inserts pose serious problems for shooting IR if I don't want to bring a changing bag. 3) Polaroid backs are much, much cheaper for the Mamiya. I have shot a bit with the Mamiya, and it's very nice, but it feels a bit plasticky compared to my tank-like pentax. So I was wondering if anyone could comment on the reliability/sturdiness of the Mamiya body. I don't really shoot any AF. I just happen to be able to buy a 645AF body cheaper than a 645 Pro and an AE finder.