For screen samples, just call the manufacturers and request them. They're free! Dalite sends out the largest samples, and I could never reach an actual salesman from Stewart. Try Draper and Vutec also. I ended up with Vutec Brite White (1.5) after playing with the samples and seeing an installation with it.
Going with a 4x3, 16x9, 1.85x1, or 2.35x1 screen is purely a matter of preference. You will find people in this forum with all of these and numerous ways to get a 16x9 or 4x3 image within them. However, if you have a 16x9 native projector like the Sony 10HT, you should go with a 16x9 screen for the ease of configuration. To answer your question about partially rolling it down, you could definitely do that. Some motorized rollups have built-in aspect ration control performed by rolling the screen up and down, maybe in conjunction with a masking layer.
[This message has been edited by anson (edited June 07, 2000).]