Screen Size & Gain for Sony 1031Q

I'm setting up a 1031Q with an Iscan Pro in a small (11'W x 15'L x 7'3"H) dedicated Home Theater room. It will be used 80% for 16: 9 DVD's and 20% for 4:3 VHS. Light will be controlled - no daytime TV watching; nighttime only. The ceiling will have some Sonex sound panels to absorb sound and also to reduce light reflection. Walls are a flat dark green.


I'd rather have quality over quantity and last night set up a 50"X67" ( 7' diagonal) Matte White 1.1 Da-Lite screen. Because the room is only 11' wide I figured the maximum I can do is seating for 3. At 114" distance to screen and 40" off the center the maximum view angle is 20 degrees or so (for the person sitting at either to the left or right of the center person).


Questions:


1) Is 50 X 67 too big a screen? Or should I go down to 43 X 57 ( 6' diagonal) ?


2) Given the rather narrow view angle, how high a gain screen can I use? The 1031Q is a small projector so it doesn't throw a lot of light, and after Video Essentials last night it now throws out even less : ).


Thanks,


Pat Lee