Dedication and commitment have many faces ...
Mongo, why would the 80-400 be better for this event than the 200-500?
Not that lens per se but the focal length would have been better. A wider than 200mm end on a lens would have captured more shots as Mongo managed to get very close at times (closer than he had anticipated would be possible). Having said that, the 500mm end was a very good length but would not complain if it had gone to 600mm instead. Some of the shots had to be cropped 50-70%+ due to long distance from the subjects. For this last reason, the 800E was used instead of the D4s - Mongo finds it better for heavy cropping.
So, if a dream focal length lens could have been had for this (and probably many other similar events or just for ridiculously broad versatility), a theoretical 80-600mm would have been better. However, there is no such thing and this statement will only flair up a lot of speculative wish lists.

the 200-500mm did a reasonable job and no real complaints.
PS - on this subject, forgot to mention that Mrs Mongo was shooting right along side using an older 50-500mm sigma and a crop sensor Pentax body. Effectively she was using the range 75mm -750mm. Looking at her images later, it is clear that she did not miss a thing using that combination focal length.