I have an optech padded strap on my M645 with prism finder. It's just about OK to lug it around all day if we're out walking. I certainly wouldn't want anything heavier. I also shoot 6x6 using a nettar and yash TLR. I can't really say that I feel that I am losing much on 645. Of course 6x7 is that much bigger again. Horses for courses, but I find M645 a good compromise when I want SLR. Lightweight in MF, that Nettar takes some beating though!