I wouldn't be using that ISO 32000 or higher, except *maybe* on a Disney dark ride.
On my D750 -- ISO 3200 was my top for top quality... ISO 6400 was plenty good enough for most of my shooting, and I could live with ISO 12800 if I really needed it.
While I'd still keep ISO lower when possible, I have no hesitation using ISO 6400.... and for casual and family photographs, I think I'm even ok with ISO 16000 on this camera.
At medium and high ISO, DXO gives the A7riii about a 1-stop dynamic range advantage over the D750, and a tiny advantage in noise and color. All really combine in terms of high ISO IQ -- looking at the images above, more than noise, in the ISO 16000 image, you are seeing poorer colors and dynamic range. so putting together the pieces, I feel like I got another 1/3rd to 1/2 stop improvement compared to the D750, which is really darn impressive at this level. (I was really expecting more of a break-even).
On the 24-105 lens, the hybrid OIS/IBIS works incredibly well..... which will also bring down my ISO in a lot of situations.