If 3x shortcut is disabled in 600D is not possible to use DISP+ZoomIn to go to 10x zoom. Only with Magic Zoom OFF 3x - 10x zoom can be used.
I can confirm this. Magic zoom just pops up and the zoom in and zoom out canon dialog never shows. With magic zoom off it zooms in. Also I had to hit + twice to zoom back out in canon 5/10x... I don't think it even went to 3x.
5/10x is kinda meh for video... silent pics seem only taken on 5x, Would they be sharper but smaller at 3x? Maybe its all the same data just scaled a different way.