Screen Mfg companies usually offer 16:9, 2.35:1 (Cinemascope), and 2:1 screen sizes. I prefer a 2.35 screen as most of the good movies are in this format, and I hate black bars on the top and bottom of a 16:9 screen. The new Panny has a built in feature that adjusts for a 16:9 and 2.35 screen, so in my opinion, you would be better off with 2.35, then you have the best of both worlds.
The displayed image size has to do with throw distance, and where you have the zoom set. Most projectors have a 2:1 Zoom, so at any given throw distance you can basically double the image size from the lowest zoom to the highest. You don't want a HUGE screen if your going to sit close, you will be darting your eyes left/right and getting headaches.
At 13 ft (front row) and 16ft (back row) my image is 130" diag for 2.35 movies and around 96" diag for 16:9 television.
