Jim, let me suggest also considering the mamiya 6/6mf. I have a couple of those and prefer them, ergonomically, to the mammie 7 just because of the collapsing lens mount. The only things I miss on the 6 are the multi-exposure and of course that one superwide lens! Anyway, for photography on the go, these are just wonderful. They handle just like a 35mm... with a giant viewfinder. But Suzanne is right that the lenses aren't fast enough for some available light stuff. Though I can report that pro z shot at 3200 or delta 3200 shot at 3200 are quite nice, if you want to do really low-light stuff, 35mm is going to win on lens speed alone. I have a 50/1.2 and some 35mm bodies that I use when I want to scratch that itch.
My experience with handholding the mamiyas is quite different from what Luis reports. I have plenty of printworthy shots on the 6 taken at 1/8 or 1/4 and even slower. There is a simple trick for going to long handheld exposures: use the timer. That removes the finger impulse which permits you to focus on stability. Try it.