Eventually anyway you will have to organize bookmarks at that large amounts with Opera desktop version. The first thing to do is back up that many bookmarks especially the quick dials which are bound to a specific new installation. With desktop opera syncing, then export all to a .html backup. Then clicking folders selecting sort alphabetically, also doubles after alphabetically sorting show next each other and can easily be sorted out. Make sure before this many bookmarks sorting with desktop version of Opera to have the backup. It's best to do this once a year or so.
