The setup I've gotten used to is setting aperture and SS, then using auto-ISO, but using the dedicated exposure compensation dial to essentially control ISO. For example, if I have my camera set at f/4, 1/250, and the auto ISO says ISO800 will give me a neutral photo, I can then dial back a stop of exposure compensation and it will switch the ISO to 400.
Essentially this allows me to control ISO when I want, but also just let the camera decide at other times. I usually allow the camera to run from 200-6400. Though if I'm consistently hitting 6400, I'll usually adjust aperture or shutter speed. But ISO 6400 looks pretty good on the Fuji for most types of shooting, so I don't worry about it too terribly much. The only real noise I ever see in that scenario is in almost black areas, which is pretty easy to remove in post if need be.
If this is ISO5000, why wouldn't I just let the auto ISO on the camera run wild, letting me set aperture and SS at whatever I want?
Now, with my D7100, I have to generally try to keep it under 3200, and preferably under 1600. With my old 7D, I had to really be careful to keep ISO under 800. Heck, I could even see the difference between 100 and 400 on that thing.
But the X100T and D600? Nah, don't even have to worry about ISO at all all the way up to ISO 6400. Like not even a concern at all.