My take was the images of sandhill cranes were very distant - maybe 300+ yards away - and were in relatively flat light with a high ISO. As a result, they showed very little detail. Without sharp or glancing light it's hard to see detail in a sandhill crane - especially not at that distance. Plus you introduce the additional variable of subject motion.
When I evaluate a lens sharpness I want to see maximum detail in order to see falloff or where detail starts to fade. That's why I was testing at 17 feet - near minimum focus distance for the lens.
I've been comparing both these Nikkor 800's since July, with the aim to test not only the primes but the "TC-Combo's" at different distances on real subjects. And in conditiosn in which I typically use these lenses: so handholding the 800 PF but 800 f5.6E on a gimbal or otherwise a beanbag (on a firm table). Building up the data has been contingent on time and especially the right time of the day. Unlike inanimate test charts, my key subjects are my three cats (who don't rarely obey me if at all) especially to lie in one position over a period of decent light to change lens, TCs etc.
I also am fortunate to have a flock of Helmeted Guineafowl, whose visits are often ideally timed in the golden light but the shadows are too dark where they choose to sit and preen. It's also rare for one bird to stand in one spot long enough so I can switch the Z9 across lenses etc - let alone stop motionless to get decent images! Getting shutterspeeds faster enough to freeze movement is yet another challenge..... The biggest challenge is keeping ISOs low at this time of day, with high shutter speeds to freeze movement.
However, I've built up a decent series of images from 11 - 50m distances. (And yesterday, my new pair of Nikon 10x50 Laserforce bino's arrived. The integral laser rangefinder is extremely useful to quantify distances.)....So I will share some results soon.
One clear finding is anything further than ~40m for a chicken-sized bird or Felis domesticus is far too far even with 1600mm. This is either at f11 or f13. So I cannot see the point of presenting images of birds - even as large as cranes - taken at extreme distances. It doesn't prove much, except the overwhelming influence of atmospheric conditions (as Bruce and many others have explained). This atmospheric factor is pervasive: across water, including marshes, warming rocks or bare earth etc. However, in favourable conditions on larger mammals, one can use a 800+TC for distances out to 100m or me. But I find this is the exception.
It is beyond doubt the 800 f5.6E FL is the superior prime. As Nasim Mansurov pointed out (in the Socratic dialogues in the above review), we are not surprised. My testing confirms its 1000 f7.1 reach with the bespoke TC125 gives one 2 unique lenses in one. However, the higher optical quality of the ZTC14 and ZTC2 has the advantage over the equivalent F-mount TC's. So it's tricky to draw hard conclusions. Above all, too often atmospherics trash any advantages of any of these combinations. They become basically unusable in these conditions. But in ideal conditions, no other combination can outperform an 800 Nikkor with its TC14.