Does factory reset also wipe out any installed updates? There are reports over on WPCentral that a factory reset improves performance...There are also conflicting posts regarding just what factory reset does?
One of the things that is not retained on a reset is your Office RT update from "Preview" to full license. Not a big deal, but you do have to go back and re-download and reinstall the update. It's over 500MB, so it takes awhile.