Thanks for your comments. Cropping is moderate on the big Pileated, medium on the rest, necessarily heavier on the smaller birds such as the Lazuli and Goldfinch. The Lazuli was a mistake on my part, at ISO 360 I should have mounted my D7000 for its cropping advantage. I had it around my neck with a body cap on it, so I should have thought it through more clearly and mounted the DX camera which has more pixel reach and at that moderate ISO has very good IQ.
I am still working out when to optimize by switching cameras. Intuitively if it is a larger bird and I can get adequately close, the D4 is my better option as it is just as pixel dense as my D7000. For those smaller target birds though, I think a DX camera is going to be my better option unless the light is terrible, otherwise I will need to crop the D4 too heavily. Action is probably best on the D4 too, but distance is a factor sometimes there too. That is why I would also like the D4 autofocus in a D400, which I feel the pixel density is bound to be more advantageous even than on a D800E. Hey, how about a D400E without optical low-pass filter while we are at it