I got a chance to try D500 with NIkkor 200-500mm f5.6. I've not seen pictures yet since my laptop does not fit xqd card, and my friend forgot the card reader to bring. We plan to check all images tomorrow.
Hard to compare since it's unknown camera, but the first impression was very positive. The release button is so sensitive and quiet, and the burst is so fast. I know that I missed lot of shoots, especially when panning, but it's because of the lens weight hand held, mostly it will be motion blur, I believe.
The ergonomics however is great, the grip is deep and comfortable, and the lens is very comfortable to hold. I enjoyed it first half an hour, then my arm got tired.
Which is bad is the fact that now I want 500mm lens