Hi Bill It appears that unless there is a shift in technology, DX has hit a plateau with all recent Nikon cameras in DX mode. Either native cropped sensors or with masked off FX sensors, there is little difference in DR or slope from 200 ISO and up. It is nice, and expected, that Nikon leads all others in DR, whether entry level, enthusiast or pro models.
The most surprising is the D90 for hanging with the newer models DSLR DX mode. That might be the reason for the either delayed or shelved D400. Without an improvement over the D7000, it would meet more sales resistance if frame rate and some extra buttons were the extent of the benefits.
Another interesting note is how brazen Canon is for spec'ing their 1Dx to 204k ISO where it generates a whopping 0.26 PDR. Pushing a couple stops in post with a D600 or 800 would result in more visible tone range captured above 25k. Stan St Petersburg Russia