Don, you did a good job of listing the major differences. I don't think I can add any more except that many of the buttons light up on the Tyros to show you what variation, intro, ending you are using and when loading a custom style, if there are no lights in variation 3 and 4 it means that you don't have to waste your time selecting them because there will be no change.
George Kaye
Kaye's Music Scene
Reseda, California