I use both, mainly for sport photography. Whilst there is a difference in the focus and quality dept., it is not (to my humble opinion) that big to justify such an upgrade.If I were you, I'd wait another year or so, for the D7200 \ 9300\ 400.It's just not worth it, because all in all, the difference is not that huge, and you'd work hard to find it.One more thing, the D7100 does requires better lenses than its predecessor. I replaced my Sigma 17-70 2.8-4 and Nikkor 70-300 4-5.6 with 17-55 and 70-200, both 2.8, because the image quality was ruined by the sensor. It simply demands it. When I look today on the photos I took with the old lenses, you can really tell the drifference, so it too sould enter the equasion.If you had a D90, then I'd recommend it.