I would agree that at lower ISO the increased dynamic range of the D7000 and D600 might have some advantage in some shots, but is less noticeable than the ability of the D3S to retain detail in all shots at 6400 ISO and above even downsizing the D600 and D7000 images to 12.1. MPs. That is my opinion of course.
There are other benefits to the D3s in terms of FPS, buffer, etc.
I don't think the IQ of either the D600 or D7x00 are clearly better than the D3s, depends what you are shooting.