Found a video of M90 and M91S compared with text and with pictures, the M91S is slightly faster but not much
http://v.ku6.com/show/14z-SD4048YXl_Sf.html
However I find the picture changing to be somewhat irritating, inverting the picture a couple of times every change, I wonder why, I dont think it is to clear the screen from the previous picture because then it would be the old picture that was inverted right?