I'm not that delighted I switched from the D7000 to the D800, but for my wife's work shooting weddings the D800 ability to shoot high ISO is essential. (And using the same bodies seemed sensible.) I really miss the 10-17. I don't care if it's not as sharp as the 10.5 (which I sold), it's certainly sharp enough for commercial work. I miss the size and weight of the DX housing. I only shoot wide these days; I'm not fond of the fisheye look but the Sigma 15 is a good lens. I have the 16-35 behind the Nauticam 230mm dome with 70 extension and it's ok, but my corners never seem that great, and it's a huge heavy rig like that. What I like best is the ability to crop drastically and still have a commercial file. Really, the ability to crop makes the 15 Sigma a 10-17 equivalent if you want.
I hanker after something smaller, maybe that uses the 15mm Nikonos lens.