OP is designed to work with ONE page column width (960px) and can not be customized. I have "hacked" the css to make my pages show at 1200px on desktops using responsive CSS but this is a GIANT pain in the butt. The Live editor does not like these CSS Hacks and so I have to ALSO hack the Live Editor's CSS to play nice with my 1200px layouts.
I'f I can Hack it with CSS, you guys can certainly make this a basic feature in the general settings.
Please, Please, PLEASE implement Custom Page Widths that we can set in the OP general settings and every element on the front end AND Live Editor play nice together.