When figuring max width, you should really figure that width using 16.9 dimensions, not 2.35. Vertical screen height will have more of an effect on your vision (negative) than width.
I sit 12' away from a 8' wide 2.35 screen. I sized my screen for a 'comfortable' vertical height and have been extremely happy with it. Some folks bitch about the black bars to right / left when not viewing 2.35 material, but if your room is dark, I don't mind at all. Certainly not enough to spend the money and curtains.
Be advised that 2.35 CIH set ups do come with extra costs. I think they are worth it, others don't....
