If you are wondering whether or not you can gain another level before the final fight, here is how much XP is still available:
Cyseal: ~40k XP
+10k for Arthu, if he is still alive
End of Time: ~50k XP
This includes killing Icara,
which will prevent you from saving her sister and forces you to fight against her
and that you have killed the horde of imps earlier.
The elementals don't give you any XP, so don't even bother attacking them.
Silverglen: ~ 80k XP
Sacred Stone (town and prison): ~150k XP (You will have to kill the prisoners without opening the doors.)
Hilberheim: ? (I have just killed the neutral groups right after trading with them, so if anybody knows how much XP they are worth, please let me know)