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mikew I have no scientific answer to your question. I've had the D7200 long enough to say that the biggest difference I've seen in practical terms is the buffer size. I have gotten bird in flight shots that would have been more difficult or impossible with the D7100s limited buffer. Also, I really do think the dynamic range is better. I seem to be able to pull a little more out of the shadows and blown out brights.
The Tamzooka is not as fast as I'd really like on either the D7100 or 7200. I'm not putting down the lens, I think it's pretty darn good for a 150-600 that costs only a tad over $1000, but I think the limiting factor with that lens is the lens itself. I was shooting birds with my Nikon 300mm f/4 with 1.4 TC yesterday and I realized how much faster and more accurate this lens is than the Tamron. And, the Nikon lens does seem to perform even better on the D7200 than the D7100.
As far as low light, though, I was able to focus on a baby owl in a very dark tree hallow with no problems using the D7200 and Tamzooka.
PLEASE remember that I've only had the D7200 a short while, and these comments are based on only a few outings.