Honestly, I think if you're applying to round 3, it has to be in your mind that the likelihood of acceptance is going to be small unless you're clearly above the grade in most of the categories of your application. Even then, there's no guarantee.
As other people have suggested, I think the choices in round 3 are much more about filling out the class than merely taking qualified candidates. I'm not sure if that means "we need more int'l kids" or "we've got too many accountants" or "our average GMAT is low, just take some really high GMAT kids" or what, but it seems to be fairly acknowledged that Round 3 is not approached the same way as previous rounds.
If Duke is looking for 450 kids, and they've got 420 deposits by the time interviews for Round 3 are finished, they're really only going to be looking for 30 kids between the waitlists and the Round 3 applicants, whether there are 50 round 3 applicants or 500.
My understanding is that's probably true for most top schools.
It's an unfortunate reality of Round 3, but a fairly well-documented one. It almost surprises me that there isn't a "PROCEED AT YOUR OWN RISK" pop-up when you select round 3 app.
That being said, of course, good luck to the round 3'ers! If it doesn't work out, go EA next year and you'll have a much better shot!