A high school gym would be another example of sports photography where you would need the higher ISO to get the shot. Gyms seem really bright until you actually try to do some photography of a basketball game. I know some people will put on their flash. But there are a couple problems with this. First, the effective range of the flash will be roughly 15 feet to 20 feet. Second, you have the whole inverse square law thing going on of how fast the power of light falls off. Third, you can actually freak out the players and affect the game if you are popping flash on the sidelines. But if you can shoot a higher ISO then you are golden.
Did you say auto ISO??
I have made some 16 by 20 prints of the high ISO images like what is in this article and they look even more stunning in print than they do on the computer screen. If you have never gotten a large sized print of any of your work I highly encourage you to do so. There is something so amazing about how it will look in print!
This is a really good feature when you are shooting in a fast moving environment with quickly changing lighting. The football field in our town is notoriously unevenly lit. It changes by as much as three full stops from center field and the end zone. So if you have a fast breaking play you can easily be off on exposure if you are trying to set it manually. So as much as I like the control of shooting in manual, there are times that the camera is just much faster and more capable. And with auto ISO it can work even better for me.
Picking a camera for ISO
Once you have it narrowed down to two or three cameras then go to a camera store with a memory card in hand and shoot some photos. Or if you have friends that have the cameras you are considering get together with them and get some sample shots. Shoot at ISO 100 and 200 and 400 right up to the top of what the camera will do. Another option is go rent each of the cameras for a week. Run them through the paces. Shoot at all different ISOs and in all the different situations you regularly shoot in.
Don't forget to consider other features of the cameras too. For example, if you are doing a lot of sports photography and want fast frame rate along with the high ISO then you would very well maybe lean to the Nikon D500 with 10 fps, a buffer of 200 raw images, and max ISO of 1,640,000 (yes I typed that in right). If you don't need fast frame rate maybe the Nikon D7200 will do just fine. Also, if you are going to use auto ISO how does the camera implement the feature? Is it going to work how you will like? So consider all your needs.
The other thing to remember is that there is some really good noise reduction software to help in post processing. The noise reduction feature native to Lightroom is actually pretty darn good. But there are some other third party products you could consider too. But one of the things that will happen when you apply noise reduction is the image will always become at least a little less sharp in the process. That is not a bad thing per se. And I have even used noise reduction as a skin smoothing technique in the past.