I don't think there is a cap. Hear me out, here. I made a character on another server and spent about a week there, leaving my main character to lounge out with a stack of books in an inn. Returned to my main character to catch up on my story quests with the exp going to my botany, which was level 46. Did a mess of leves to make up quest xp differences which are pretty big after level 30. I still have a full blue exp bar on my level 50 classes. I don't know how much rested I've accrued but it's alot more than a two levels worth.