Possibly - but I'm still intrigued as to why an image from a D800 suddenly loses IQ when you use crop mode.
I was under the possibly misguided impression that all crop mode did was to switch off the unused pixels leaving a chunk in the middle active.
However in order for the image to be identical in every aspect to one from a D7000 as sk66 suggests, it must surely lose aspects of IQ.
Unless of course I'm doing the D7000 a dis-service and it is a better camera than I thought.
This seems to form the basis of sk66's opinion and would suggest that anyone not needing the "width" that full frame gives would be much better advised to spend their money on a used D7000 and blow the change on (insert own indulgence here).
cheers, cw
One last attempt:
A crop doesn't change the performance of the sensor in any way... it doesn't matter if it's done in camera or in post. What DOES change is the resulting IQ of the final image and what you can do with it. This should be obvious to anyone.
This is the problem with "the ratings" etc... You have to understand that the performance ratings (DR/ISO/everything) are relative to every other camera when using the *entire image* to do *exactly the same thing.* The D800 is rated much better than the D7000 because you are using 36MP to generate an 8x10 compared to using 16MP to generate it. If you crop the D800 image down to 16MP (DX) you would then be comparing 16MP vs 16MP to create an 8x10... the D800 would perform/rate much worse in the comparison because you've thrown away 1/2 the image/data and you've removed a large portion of it's advantage. It would rate/perform very much the same as the D7000.
The performance ratings of the sensor are for the entire sensor combined... they are not for a portion of the sensor nor "per pixel."
Not understanding this leads people to think they don't have to worry about composition or using a longer lens. They think they can just crop the image and still get the same performance from the sensor, but you can't. (at a pixel level you can, at a final image level you can't)
The D800E/810 have an additional "advantage" in that they've modified/removed the AA filter which can allow the camera to resolve finer detail assuming the AA filter is the limiting factor in the image taking process. This advantage is more significant when displaying the image at closer to 1:1 and it is less significant when downsampling.
When comparing the same generation of technology a FF sensor will always win over a smaller sensor because it is using a larger area to collect more "information." And in low light larger pixels on the same size sensor will always win because each pixel can collect more "information."
There are both advantages and disadvantages to using a larger number of smaller pixels... There are reasons why the top cameras for action/low light (1Dx/D4s) are under 20MP and it's not because they couldn't have given them more. And there are reasons why one would choose a D800 over a D4 irrespective of cost.