#3. "RE: What should I consider in a D800 with lens?" In response to In response to 0
If you want to consider lenses that cover the focal length range of you Sigma 10-20, you might want to have a look at the Nikon 14-24/2.8 or consider one of the excellent Zeiss zf prime lenses lenses, 15/2.8, 21/2.8 or 25/2. These lenses are all of very high optical quality which I believe you will need to fully realize the potential of the D800.