I have a pentax 645 and a couple of 35mm's. I can not consistantly shoot 1/30 handheld without bracing against something with either system. The 645 is bulkier but I find the ergonomics good, and from eveything Ive heard the 55mm for it is wicked sharp. As an aside I'm thinking about getting rid of my gsn and perkeo 1 w/ vaskar lens to finance a spotmatic. Reason simply ergonomics