"Best" and "Luxury" are highly subjective terms especially when you are talking about this much money and how strong a preference you have for a gated community.
If gates are a must then don't bother to look south of Disney. Celebration has no gates and never will. Reunion is a massive gamble if you want to spend this much money (might as well go to Vegas and play roulette). Formosa Gardens is the only other gated place south in this price range, but you will hate the view,
Immediately north of Disney you will find a number of very good choice. Check out Keene's Pointe, it may well be what you are after. And of course any thing with Windermere in the name. Here again, as with Celebration, gates may be a problem. There are some pretty nice places without gates.
However, my point in answering this question is to give you a totally different idea. Check out Lake Nona, which is well east of Disney, but due to to the 417 expressway is actually only about 25 minutes away. No one ever thinks of Lake Nona as near Disney, but in terms of drive time it's actually just as close as a lot of places to Disney north which have no fast access, just busy streets with lots of stop lights.
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PS. If gates aren't mandatory, then hands down you want to be in Celebration.