I think there is a glitch involving the xp with Winterbane. I didn't check how much exp the dungeon gave me the first time I did it which was a rank 5 dungeon. I went into the rank 11 dungeon and the quest gives me 24898. I doubt the first time the quest would give me double that so those that mean every rank of the dungeon counts as its own dungeon and gives its own exp? If this is true then you can get some pretty high levels by doing everything of the dungeon twice.
Also you can skip the second fight on the first floor by just walking to the ladder.