I current have a Da-Lite pull-down 52"x92" matte white screen, and it has pretty bad waves. It's tolerable (barely) when viewing from straight on, but when viewed even a little from the side, it's quite distracting. I previously had a pull-down 60"x80" hipower, and I never really noticed any waves on it. When the lights were on, you could see that the screen wasn't perfectly flat, but I never noticed a wave when viewing video. The matte white is much worse in that regard.
Dave