#2. "RE: need buy a camera. D7100 or a D600 ???" In response to In response to 0
What, if any, lenses do you own from your D80 days? If you have a good collection of DX-appropriate lenses, are happy with them, and are looking for an affordable re-entry, then a DX body might be the ticket. Otherwise, your options are more open.
If I were starting completely over, I might go FX. But I appreciate some of the advantages of the DX bodies, especially for tele shooting.