What is the most gain on AT Screen

You wont find a AT screen with 1.4 gain, highest Ive ever seen is 1.2 but most are lower. You will not fill a 140" screen with the 8000 in best mode.

It will be bright if you dont care what the colour looks like, "best mode" will not be bright enough, you will have to use one of the video type settings. The highest gain AT screen is a 1.2

You can go to 140" scope with a AT screen if you use one of the new JVCs. Im using the new X95 with a 150" AT scope screen but I dont use the lens memory I use an anamorphic lens. Check out my HT in my signature, you will see the screen.

Here is a formula that you can use:

Achieve at least 16 foot lamberts brightness in calibrated, 'Cinema' mode assuming you have a completely light controlled room (higher brightness if this is not the case). This is calculated as 'lumens/screen area (sq. ft.) x screen gain. You will need to find what the calibrated brightness of the projector is in lumens. For the Panny, 'The PT-AE8000 measured 602 lumens calibrated in "best" mode' according to ProjectorReviews.com

So, your maximum screen size will be: 602/16 x 1.2 (assuming the highest gain screen possible) = 45.2 sq. ft. or a 122" diagonal (16:9)

If you use an anamorphic lens for a 2.37 screen, you will get away with a 124" width by 52.3" high (134.6" diagonal) (This factors a 10% brightness loss due to the lens, although good lenses lose much less light).

You may also factor in bulb dimming over time, so your screen sizes will be even smaller.

If you have the $$$, Stewart has some high gain screens with perforated options.

http://www.stewartfilmscreen.com/residential/materials/3d/silver.html

http://www.stewartfilmscreen.com/residential/materials/3d/silver5D_residential.html

http://www.stewartfilmscreen.com/residential/materials/3d/Reflections_Active_170_3D/Reflections_Active_170_3D.html