The morning EMH really help alot. Will you be able to do a whole, maybe. We go at NYE, which is about as crazy a crowd can be. We will hit the morning EMH and you can really see a difference in crowd level the first 2.5 to 3 hours. After that it is really nuts and time for us to go back to the room or hit lunch.
Our kids are older teeneagers and we also take advantage of some of the late magic hours. For example, on Dec 30th Magic Kingdom is open until 4am.