Bill...I have the D610 and D7100... Go FX and don't look back....The pro-dx will probably be so close in price to the D610 that it would only make sense to skip it and go fx...
This is what put question marks in my head.
I get the reasoning DXXX for FX and DXXXX for DX, wait and see though ...
From the D7000 I had in mind to complement with a second hand body later, till now that would be a second hand D800E or maybe D6X0 or Df; so FX seemed obvious.
Now with a possible high end D9x00 DX body I´m not convinced anymore.
FX: Different use of the 50mm and 70-200mm which would give a FOV that can be used closer.
=> I´m convinced that for portret the closer use of the 70-200 would give better results; however that is not my favourite theme.
DX: I keep the multiplication factor, I can use all the lenses I have.
My internal questioning is that I´m not convinced that the portret advantage of FX (using lenses with less deformation issues, like a 85mm or 105mm) can not be solved with Lightroom lens corrections, for my usage. So if the D9X00 gives a DX ISO performance of 2900 or more on DXO Mark and some more pixels so I can crop more, I do not believe I will go for FX.
I found the D800 too expensive in renting, it seems to me I would rather buy second hand and if I do not like it sell again. So I seem to go for buying a D9X00, probably loving it and never going to FX. I would be going from a DXO score of 80 to a around 90 score anyway, would be great for a "pure" hobbyist like me.