I find 645 is a nice nexus between sharper lenses and larger working apertures, with sufficient film real estate to not be bumping up against film grain and resolution limits, as one can easily do in 35mm. Pretty much all formats from 135 on up are capable of making decent sized enlargements. It's actually easier to handhold my P645N than a 35mm SLR to achieve critical sharpness throughout for big prints; I get tack sharp results often to silly slow speeds like 1/8s, not every frame sharp but a sufficient number of keepers in environments where I could not take a 4x5 or a tripod (and certainly would not have time to set up and take down). Not waterproof but the P645N is pretty well bombproof and snow resistant-- it's my first choice for snowshoeing and XC skiing jaunts in the mountains, for instance.