I just upgraded from a D70s. Luckily, I had a 17-55 which afforded me the opportunity to basically choose a D7000 or D600 for almost the same price. I decided to dump dx and go fx.

That said, the D7100 does not seem like a huge upgrade to the D7000, and really doesn't differentiate itself from the D600.

The only things it really has is the no-aa filter and the newer d800-based focusing.

That said, 39/9 vs 51/15 doesn't really matter to me. They're both a lot of points and a lot of cross - types. And both still cover just the cropped area, so neither is going edge to edge.

Visit my Nikonians gallery.