I have a Hasselblad and RB67 system. I also had 645 systems in the past. I love my RB and I love my Hasselblad. Never liked 645. I have no problem carrying the RB67 with a grip for hours and using it purely handheld, I can easily shoot it down to 1/15. Ok, it can get a bit heavy after 4-5 hours but when I get the film back it is superb. It also makes my Hasselblad look small and light. Somehow I tend to pick the RB more often than the Hasselblad nowadays.