I recently finished three main story quests (Drowning out the voices, acting the part and dressed for conquest) which are marked as lvl 46 quests.
However, I could finish them being level 45, and said quests come right after the level 44 ones. So I guess they are not really level 46, but 45.
I might be wrong... but I have never been able to accept a quest which requests more level than I currently have.