And while we are on the subject of high ISO, I hope you will permit me a slight diversion.
I did some field testing (ok, backyard testing) of high ISO, Image Stabilization (IS) and post processing for noise last weekend, using a still life subject for easy comparison. In my personal - albeit limited - experience - I found that both body and lens IS enabled was advantageous. I noticed a distinct reduction in the "wobble effect" during composition; I could composed better - handheld - because the scene in front of me wasn't so jittery.
Regarding image noise, I shot as high as 3200 ISO on my Olympus EM5 Mark III. And while the noise/grain is apparent, I recall far more grain when I shot 3200 ISO film back in the day.
I also find it helpful to think of digital noise as film grain - then it becomes an artistic choice rather than being at the whim of the sensor...