If you are worried about brightness, but you also need a retractable screen... I would recommend that you look at the Da-lite Hi-Power (2.8 gain!). It does a really great job of boosting light levels. The main drawbacks are a narrow viewing cone (which shouldn't be an issue in your narrow room) and slightly elevated black-levels. However, I've been using these screens for years and never found black-levels to be an issue... and your PJ will have much better black levels than anything I've used. The benefits are great:
1. Really bright (2.8 gain)
2. Rejects ambient light outside the viewing cone (so light from the PJ will be amplified, but light from a side window will not)
3. Minimizes the appearance of waves (which is a huge problem with retractable screens... especially big ones like you want -- unless you upgrade to tab-tensioned for more $$$)
By the way, one more thing... the screen is 'retro-reflective'. Which means it amplifies the light in the direction of the source. So it
actually will amplify light from a window, but it will do it back towards the window, not towards the viewer. That means if you use ceiling can lights or side lights the screen will also reject them well for the viewer. But, if your PJ is mounted on a tall ceiling, you loose some of the brightness benefit as it will be amplifying the light back toward the PJ (ceiling). Ideally, with this screen you would want a wall mount a few feet above the viewers heads. I'm not sure if your long room will accomadate that, but a ceiling mount with a long pole to drop it would also work.
http://www.da-lite.com/education/angles_of_view.php?action=details&issueid=29There are other reflective screens that work more like mirrors (meaning the light will be reflected and amplified at expected angles) and your room is actually well suited to that if you can use a long-throw setup with your PJ. If you have a short throw (PJ close to screen) the angles and lengths of the light paths will be very different across the screen, which usually leads to darker sides (or uneven brightness if you are seated at the side of the room). However, the further you push the PJ back in the room, the less of a problem this becomes.
This stuff is a pain to write out... if you want to chat on the phone/skype sometime, just PM me.