D3 and D500 are completely different animals IMO i do not know much about the D3 though.. for those of us shooting DX already i think it would be a pretty big improvement at least in the less noise at low light area..
most of what i am seeing from the D500 is excellent.. i have not seen allot of high ISO photos though. i have saw a small hand full taken at 51,200 ISO and there noisy but not horribly noisy, those photos have more noise in them than i would like to see but that is at 51k iso which is crazy high and i would have expected much worse to be honest..
now i do not know what kind of lens these people are using in all of those excellent photos or how they would have turned out if they were using the D7200, some some of the photos that are excellent could be a really high end lens.. or maybe not. i see lots and lots of excellent photos out of the D7200 would it really be worth all that money to get a camera that does better in low light and shoots more FPS, for me the answer is no.. i can shoot at 10k iso with my D7200, sometimes the photos have a bit more noise than i would like, a little noise reduction on those photos usually does brings them down to a acceptable level of noise for me..
what i would like to see is someone using the exact same lens and taking photos of the exact same thing with the D7200 and the D500 to see if there is a noticeable difference in image quality in good light..
i would also like to see the same thing done with higher ISO shots with those 2 camera bodys, i am sure the d500 would win but it would be cool to see. looking at the full frame vs d500 comparison with high iso it looks like they do just as well as some full frame cameras to me when it comes to the high iso..
but check this out.. this is one of the high iso photos i have seen.. <a data-flickr-embed="true" href="
Kitten by Ken Wheeler" title="Kitten by Ken Wheeler"><img src="
https://farm2.staticflickr.com/1650/25986877614_1797cc1c13_b.jpg" width="1024" height="683" alt="Kitten by Ken Wheeler"></a><script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>