loon: I don't think we know the answer to either the question you asked me or Tao. Could be some difference in the sensor other than pixel size but that would surely be a minor difference so I would expect the D800 sensor to have almost the same light collection characteristics as the D7000 sensor. Have to wait for a number of independent reviews of it.
One of the attractions of the D800 should be that it gives you a DX inside an FX: two cameras in one body. We will see if that actually proves to be the case.
Now there's an answer I can take to the bank - we don't really know! I will wait for the tests. Thanks to you both Donald & Tao, you've both been wonderful. This forced me to consider what I would do even if it had no better IQ than the D7000, and concluded there are plenty enough other benefits! It is exactly the pixel density I want for cropping/reach in a switchable DX/FX full frame camera, with killer autofocus system, decent buffer, 34MP for landscape which I would love to get more into but felt held back by the DX fov, etc etc... I wants it I needs it, my preciousssssssssss :)
BTW you can check out my stuff at http://www.wildbirdy.com. Many many thanks again! Sue