Re: Proper screen size for best quality picture
The screen can be as big as you like, as long as you get the appropriate Foot-Lambert amount of light on the screen (ft-L = measurement of light onto one square foot of screen). This is of course the result of the actual light output onto the screen from the pj. The target is 16 ft-L, but your local cinema sometimes falls even below 10.
The optimal screen size (horizontal image) is Seat Distance / 1.2. Meaning that if you sit 10 feet away from the screen, the screen should be 8.33' wide. This is because this is exactly 45 degrees to the Left and Right edge of the screen, which is also where the speakers should be, behind an acoustic transparent screen. All per THX cinema specs. Of course your room needs to be dark without any reflective surfaces or objects.
I have measured up several film post production stages at Sony, Hollywood and Twickenham, London, and they all adhere to these angles and distances.
So in reality, you should match your pj and its light output so that it gives 16ft-L onto the correct screen size for your room and seating lay-out. You are not supposed to match the screen to the pj!!
If you send me your room lay-out plan, I can do the calculations and drawings for you. It would also calculate the audio sweet-spot for you.