Hi, Joms. While it is certainly awesome to project the biggest image your projector is capable of doing, please keep in mind that the size of the screen is a factor of your viewing position, i.e., how far your first or optimum seat from the screen will be. If you have an overly large screen, it's like watching a tennis match at front row--you'd have to move your head (or at least your eyes) to see the whole picture. Not only is this silly, it's annoying and tiring. Ideally, you should be able to see the whole screen without moving your eyes, specially your head.
The prescribed screen height is 1/3 the distance from the best seat in the house. What I would suggest is that you plan your room layout first, measure the distance of the prime seat from the screen, then get the appropriately sized screen for your room dimensions.
Cosmotech distributes the Draper screens (look for Elsie Labrador). Da-Lite on the other hand is distributed by, believe it or, Multi-Island photo shop. Fret not because you can go to the Da-Lite website and initiate a chat with their customer service. They're very helpful.
'Hope this helps.