My screen array diagonal is atm 2 meters. At least thats what Steam hardware survey tells me and I have not exactly measured. But my two side panels are tilted a bit so I look at them in a more perpendicular fashion.
Primary Display Size: 75.00" x 26.65" (79.57" diag)
190.5cm x 67.7cm (202.1cm diag)
Anyway, about turning your head. I sit at approx 80 cm from these screens, at that distance I can use the middle three screens without turning my head, for the side screens have to move head slightly to look at them properly. While they are still within my field of vision reasonably well without turning the head, its a bit inconvenient to look at them for me without turning my head so that the screen is in focus properly for both eyes. What I like with that setup is, that I get approx the same FOV in games as the screens occupy in reality in my field of vision, which is approx 120 degrees.
So, a single 40'' screen at ~80 cm from you should be fine, but that's ofc somewhat personal, whats comfortable and whats not, but for most people it should be pretty ok. With 3 of these screens side ones would move probably outside the area where you have binocular vision with their edges. Dunno about portrait setup tho (6480x3840 16:10 screen array) thats a bit more natural aspect ratio for the eye (16/10 ~1.6 while 120/90 ~1.33). That might be still pretty decent. Humans are supposed to have binocular vision approx 120 degree horizontally and approx 90 degree vertically. Human vision system physical max resolution should be approx 8000x5000 lines (determined by the size of the light sensitive cells in your eye and the optical properties of the eye) assuming the whole vision system has the highest resolution which you encounter in the very center part of the eye.
About AA - depends on the distance you are from the screen and screen ppi ofc. When I was saying that you dont need AA at that resolution I was meaning, that to see all the screens you are sitting a bit further from the screens and as such the AA is less useful, for example, with 23'' 1920x1080 screen human with 20/20 vision should no longer be able to tell the difference between x0 AA and x16 AA as the screen should be already getting into "retina" level of ppi at that distance.
Also on related subject. While the large screen arrays are really nice I hope the Occulus guys manage to source good 7'' 4K screen with 120 Hz refresh rate and put it in their next version of that thing. Would take couple of display-ports to drive it but should be still reasonably manageable to deal with it, one DP for one eye, running at 60 Hz