If you are going to shoot landscape with movements on a 4x5, donīt worry about whether it takes you 30sec to setup or 2 minutes. I have a lovely Ebony 45SU which I believe is very quick to setup. It is just a matter of mounting the lens. Still I spend in average 20 minutes in preparation of an exposure. In my opinion it is just an entirely different realm than shooting smaller formats.
What I am saying is: You may think you need a "fast" camera, but I think you may find that you worried about the wrong parameter.
I would say go for those movements. And for a 120 back go for the Horseman 6x12. I thought I would use my 6x8 back too, but it just does not make any sense for me. And with 5cm back shift I can shoot two 6x12 frames and get a sweet 6x22 pano without moving the lens :-)