most of the front shots were around 1600 ISO, drummers were usually a stop more so 3200. i could probably go a bit lower but i wanted the shutter speed to be at least around 1/160-1/200.
what i noticed with development of new cameras, there are 2 things that have significantly improved. Smart autofocus and ISO. And R6 has a "small" sensor of "only" 20mpx so it handles grain/noise really well.
Damm 1600-3200 ISO and you got almost NOT grain, that camera is really good for that!
yes there was the time when 1600 was my limit of what i was willing to use on the 600d. on 80d it was around 3200. R6 i think if there is enough light (so i don't have to bump it up even more in postprocessing) i would probably use 8000, maybe even more. but if you are trying to use 10000 you should probably add some light to that :D