The other day, my parents bought a new TV and we got into a discussion that's applicable to projectors and screens in larger presentation environments, and even to your home computer screen. The short story is that humans perceive screen height more than width, so it's important that you don't simply replace a older television or projection screen with another based only on the measurement of the screen diagonal.
For the purposes of this illustration, a "wide format" screen or television will have a 16:9 aspect ratio (width:height), which is common for HDTV content. A "standard format" screen will have a 4:3 aspect ratio, which is common to older computers and television.
Have a 6x8' screen now? Better get a 6x10'8" screen next time. Don't get a 4.5x8'.
Televisions are sold as 19" diagonal or 26" or 42" or whatever. But not all 19" diagonals are created equal. I realize that most of you are buying projectors and screens, and not 19" televisions for your sewing room, but you'll get the point. I'm just using the math I used for my mom.
A wide format 26" television is about as tall as a standard format 19", so if you are replacing a 19" television, don't buy a 19" wide format television, unless you'd be happy with a picture that feels much smaller. Again, I realize that these sizes are much smaller than a projection screen, but you can use the ratios as the basis for your own math.
19" Standard Format has close to a 12x16" screen area.
19" Wide Format is about 9x16" screen area (3" less height).
26" Wide Format is 12x22" screen area (about same height as 19" standard).
So when you're thinking about new wide screens or televisions, make sure to get a screen that's at least the same height as what you're used to.