Sept 30 isn't that early. I already had 1/2 of my interviews by 9/30 last year. If you take Step 2 on 9/30 you will have to wait 3-4 weeks to get your score. This will put you at the end of October. By that time, many top programs will have already rejected you by your Step 1 score. I would take it by the middle of August at the latest.