II have the RRS and Arca Z1 heads, use them both frequently with a Canon 300mm f/2.8 lens, and love them both. I think personal preference and ease of use make these heads great. Sure there are many other choices. It boils down to what works best for you.
I have the 80 mp back and am upgrading to the new 80 mp back. I can't wait!
BobYIL: To see the prices of the latest 40MP backs hovering around $20K indicating to one fact: None of the MF manufacturers are expecting substantial sales quantities to feel encouraged to reduce the costs.
I'm a serious amateur and am awaiting delivery of a Phase One 645 DF with an IQ180 back. Why? Once you shoot with one of these cameras you will know the answer. They are simply incredible and the captures are that much better. By the way, notice that I said that I am waiting for delivery. The units are sold even before they arrive here in southern California.