Also include in your "calculations" that while leveling the secondary classes on lover levels that your main class you're receiving the XP bonus. Also - you can (re-)use plenty of the gear, items and gill you've collected so far which makes it a bit easier too and finally you know your ways around location, those are already discoverred and showing on the maps, you can teleport and know all the leve quest and dungeons etc. so you will get progressively faster.