500k is quite a lot. It'll outsell it ofcourse, but not by that much.
Let's assume the U averages 60k because of various game releases in September. For it to outsell it by 500k, then the XOne would have to sell around 185k a week; which is more than a 300% increase on the weekly average right now. Yes, Tier 2 countries help and Destiny will help as well; but the average will probably be closer to 120k, or doubled sales for the month. So 200-250k difference in September seems more reasonable.