I find med format to be a pretty big letdown compared to LF, not only due to neg size but general lack
of movements. And you won't save any weight except in the filmholder category. Late Pentax lenses are
quite good, esp for the going prices. I shoot a P67 sometimes for travel, windy and rainy conditions, for wildlife, or just for a change of pace from LF. It's got a pretty aggressive mirror slap, so you either
have to shoot it at fast speeds or on tripod with mirror lockup. It's like an oversize SLR and quite a bit
different than the 645. Both Pentax cameras are classics. But I personally find 6x7 at the margin of
acceptable neg size for enlarging (unless I just want small prints). 645 is just too small.