Mael you forgot the texas leicas meaning the bigger Fuji Rangefinders with fixed lens but with a good rangefinder and that fixed lens is very good. They are not as lightweight as the 6 and the GA though. Another choice would be the Bronica RF645 it usually costs less than the six and the lenses aren't bad either. The GA645 is a good camera the AF is not the most precise in the world but is still decent. The GA is also a lot more affordable than the Mamiya six. The P67 is heavy and not really a walk around camera. A good compromise between speed portability and interchangeable lenses is the mamiya c330 it's a TLR with interchangeable lenses and shows the parallax error/correction in the finder the drawback it is heavier than the six and lacks metering. The advantage is the price of the lenses, the body and its close focussing ability. Zone focussing is a bit hit and miss furthermore wide cameras are not the best choices for portraits.
My Advice would be to get either the GA645 or the Mamiya C330 both great cameras for little money.