Thinking of the 800/5.6, we have to remember that we would be able to use that with a TC too, now that the latest cameras can focus at f8! Mind you, it would certainly be a test of technique
I recently asked if the D4 and the 800mm would become the new birding combo, and mentioned that I thought the D400 was no longer that important. Many responded, and seemed to miss my point. Perhaps it was the way I worded my initial post.