Honestly, after learning 3's, backflips were nothing--literally just a balls trick. But I know what you mean about spinning--the transition between 5 and 7 was pretty small, I haven't done a 9 since last season cause i've been focusing on style, but yeah.
My biggest fear are switchups though haha. I feel really comfortable with flat 3, rodeo 5, rodeo 7, cork 5, cork 7 backflips, frontflips, and 7's. As far as rails, I can 2 and 4 out both directions, but I would still rather 270 on than switchup. They just scare the fuck out of me for some reason.