I get asked “you say use higher ISO when bouncing, if the ceiling is high. So what is too high an ISO value”?
There is no answer for that. It depends o you and your camera. My 1Dx is good, and it shows this:
12800 ISO, no noise reduction:
51200 ISO, no noise reduction:
51200 ISO, Lightroom noise reduction:
51200 ISO, Lightroom noise reduction, detail actual size (once you enlarge to real size:
So this shows that with this camera, even at 51,200 ISO, all is well and you can use this for large 13×19″ prints that look great until you are right on top of them. Even then, they look better than my pictures looked in the 1980s.
So… no worries. Be happy. I shoot up to 1600 ISO without even thinking about it. Learn what you will accept from your camera, and then live a happy life unworried by high ISO concerns.