...and what happens when you apply the same post production to the D800E sample?
Thanks to zzapamiga, we found comparable pairs of RAWs from D800 and D800E. I tried the same comparisons done by Horshack. Pixel peeping the images at 100%, I could see just the tiniest advantage of additional clarity in the images from the D800E. After applying a bit of unsharp mask and contrast boost to the D800 files, the differences disappeared.
I don't know if this is representative of what we will see from the production versions of the cameras. Nor do I know if the differences might be more pronounced with different subject matter. There were comments in this thread that the advantage of the E would be be more obvious for landscape scenes. Why is that?
My impression, until I see better evidence, is that the IQ advantage of the files from D800E is barely visible, and possibly no better than what you can get from the D800 with a couple of quick PP tweaks.