The Mitsubishi hc4000 has superior OOTB color than the Pro8200 or Optoma hd20. It also has far darker blacks. I have owned both the Mits hc4000 and the Viewsonic. I like the Viewsonic for some things, but the Mits is all around a better projector, better color, slightly sharper, better blacks, and better for movies.
The Viewsonic has less RBE, but this will only matter if you are one of the 15% or so that is bothered by RBE at 4x CW. The Viewsonic's RBE is less because of the raised black level floor (worse blacks), and maybe also helped by the extra segment on the wheel (7-segment instead of 6-segment).
You do not need more brightness for a 92" screen, you'll have too much already, even with a gray screen. You should be able to run the Mits on low lamp for a very long time.