By the E4, you mean the xy E4 right, because with the ORAS rematches. I'm pretty sure that you can't stop in-between the E4 and Steven, he's my main worry, all my guys have megas, and are very close if not over the E4s rematch leveling, meaning I'd most-likely fail over and over and over again, though I do admit I'd get a lot of EXP.