Will be watching this thread as I have the exact situation and I'm going in the same direction. My room is the same size, distance to the screen the same, my current screen the same size but the only difference is that I have a JVC RS45 projector. My current screen is a Grandview manual and like you will upgrade to a larger screen from 100 "to 120", likely somewhere in the middle.
I view a lot of 3D content and I am a little disappointed with the brightness in 3D only, 2D is fantastic . I would like to purchase a screen that though bigger by 20% would yield the same level of brightness
with a higher gain screen. If this is possible, please advise the screen
If you feel I am hijacking your thread I will move to another post. It just looks as though we are on the same mission here.