I owned the original D version and it was slow to AF and not particularly sharp. Seldom used it for moving subjects. When the new one came out, I got one and it was a giant improvement. I use it regularly with my D500 and D850 when need to limit weight and need zoom capability. I find it exceptionally sharp and very fast and accurate AF, but very expensive. I have not compared it with the 200-500 or any of the off brand models. However, it is not like my 400/2.8 in AF speed or IQ, but not much out there is equal to the 400/2.8.

I have never fully bought in to the crop factor argument though. With the large size files from the D850, I can and do crop in to a D850 image to create a result similar to the crop effect of the dx body. I bought a D500 to have a smaller, lighter alternative to the 850 and also to carry as a second body. I find the hi iso performance of the 850 to be a lot better than the 500, so I often shoot with the 850 and crop rather than 500 if light is an issue.

And please don’t let the pro/con argument about crop factor overtake the discussion of the lens. My conclusions are based on my hands on tests of what works for me.