I now this is going against the grain but ... one of the days I would go the the Studios side instead, for a couple reasons. One is that if you get there 30 minutes or so before their scheduled open, there will be few people in line (as most are drawn over to the park with EE), and you can often get right up to the gates. Then, they usually open 10-15 minutes before the posted time, giving you a big head start on the crowds. And if Diagon Alley is the priority hightail it there and it'll be basically empty.
The second reason is the huge draw for most people with EE at IOA is Hagrid's. But consistently lately it seems it has had trouble being open at that time, and many are advising planning to queue up either at lunch or near close. So keep that in mind for IOA EE, and if indeed Hagrid's is your number one plan on veering off to VC (which never has anywhere as long a line).
BTW - I assume you're staying on site, but do you have Express?