I have never really tried to capture Birds in Flight but I can certainly understand why those long bursts would be very beneficial. With the upgrade to the AF system it would seem that the D7100 would be better suited to BIF than the D7000 but without the ability to shoot longer bursts would only be halfway there.
I understand the intellectual curiosity as well, that's why I bother to read as many posts as I do. You never know what you can pick up that might be just what you need in a given situation. I am sure once a couple of people get the new camera in their hands we will quickly get the answer to your guesstimates.
Marc There are always two people in every picture: the photographer and the viewer.-Ansel Adams