I find med format to be a pretty big letdown compared to LF, not only due to neg size but general lack
of movements.... I personally find 6x7 at the margin of
acceptable neg size for enlarging (unless I just want small prints). 645 is just too small.
I think "acceptable" in terms of film format/min film size for enlarging is subjective to an extent. But then, I'm partial to smaller prints (I will say, though, that the only large prints I've seen have been college art student exhibitions, and many of them are lacking in terms of composition, emotion, and all those subjective "somethings" that I think should be in a photograph; the only redeeming quality is the impressiveness of scale). Also, I'm getting to the point physically and emotionally where carrying around a 5x7 camera is becoming too burdensome. Other than a high-end digital camera, medium format film is most likely going to be the route I'm going to have to go, regardless of what the large format master race thinks. I really do mean no disrespect, but I feel like the film size argument is akin to the megapixel and full-frame vs crop frame sensors arguments in digital photography forums or lens quality arguments or whatever else we can argue about: kinda pointless; as long as you really understand what your system can and cant do, you can make good prints with whatever you've got
"I have captured the light and arrested its flight! The sun itself shall draw my pictures!"