No matter if it's a FX or DX there is some noise reduction. FX shooters will always say that full frame is better than a crop for low light because that's what has been true for the last 10 years or so. These new crop frames are throwing older full frames right out if the water on low light, high ISO performance. New processors etc. And I would argue that the d500 would compete with a D810 in low light. NOT resolution. Shoot Both at ISO 10,000 I bet you would see more noise in the D810 than the d500. Yes resolution is different and the size of the sensor is quite a bit bigger but have to factor in pixel size. I think the d500 is only 20 or so megapixels whereas the D810 is 36!
I've shot a Sony a7 24mp full frame and a Nikon d7100 and to my eye they were pretty close in ISO performance. Yes I know one was smaller pixels etc etc, but in real life how much of a difference will this actually make? For the price and the sharpness of images you can get out of a D7100, that would win in my books. Also for the price in comparison to a D810 and features you get, a d500 might be an excellent choice.
Just because you shoot DX doesn't mean your any less of a photographer. ☺ no matter how many pixels you have.
Also the ISO range of the d500 is far superior to the D810, I think we all know that the more ISO range usually means the higher ISOs produce less noisy images.
Sent from my D6503 using Tapatalk