Like many of you, I shot with two bodies when I had the D700 and D7000. Pixel density wins when it comes to distance. Brian T said it best, it's pixels on the subject that matters. Enter the D800. The DX crop from the D800 has about the same pixel density as the 7000. Eureka! one body to carry. Then, along comes Nikon with the 7100. Resist I did, but eventually I had to take a look. Not convinced that the greater pixel density would improve the reach of the 80-400 all that much, and concerned about the IQ, I took one home to try it.
D7100 with 80-400 @ 400mm, f/5.6, 1/800, ISO 500 (Frame count on D7100 = 22, new!)
Full frame 1500x1000 pixel crop
Larger view by clicking image (do I really have to say that).