I have a 55" Mitsubishi WS HD RPTV. As some of my favorite Kubrick movies are lamentably in 4:3 AR, I have to watch these either stretched or with gray bars on the side. I prefer to watch them in 4:3 mode to maintain the proportions of the picture, but I'm worried about my screen burning in. What is a "safe" amount of 4:3 viewing on this set? Anyone have experience with this?