I guess it's time to summarize where things are in my view.
First, the significant lower quality of the D7000 image: I believe this may be due to the focusing system of the D7000. In this instance (low contrast, auto-focus) the D7000 did not get as good results as the other two cameras (granted none were "sharp"). Using manual focus all three cameras produced similar results. The first two D7000 images show the cropped original (auto-focus) and below it the cropped second try (manual focus). As has been suggested, atmospherics at 10 miles may be impacting quality in all as well as camera movement.
The following shows the entire image (it has been adjusted in PhotoShop). A line points to the place shown in the last image which has been cropped and enlarged to show pixels.
The image below is the same as the second one above, but it has been adjusted in PhotoShop.
The above is still not "sharp". However, I am wondering if, given this type of subject and at this magnification, just how much improvement to expect with better photographer skills? Looking at the pixels below, it doesn't seem to me that the individual trees can ever be made to appear really sharp. Is this correct?
I have chosen to use high ISOs because most of my shooting will be hand-held (and I need fast shutter speed to overcome that) and I need more depth of field for some subjects, such as the one below. It has been sharpened. This is was taken at ISO 1600, 1/1000th and f/16 with the lens at 400mm. I would appreciate your comments on sharpness here too.