As Brian said, the D600 only puts 10.2 Mp into a DX frame, whereas the D7000 lays 16 Mp on the same image area. In spite of the more "modern" D600 sensor I think the D7000 would give more detail in most normal shooting situations. The D600 would have an advantage in poor lighting conditions ; fewer pixels but much less noise and more dynamic range.
D800 has 36 Mp and it will put 15.5 Mp into a DX frame. I suspect D800 would give superior output to D7000 in any situation where a DX lens is used, but again, more so in poor light.