Just to further complicate things, look at this discussion of the dynamic range improvement from the 5DS to the 5D4:
https://www.dpreview.com/news/322975...to-the-5d-line
That's MAJOR. Of course, you must realize that you give up substantial resolution to get dynamic range and they're purposely under-exposing by -5EV. That's a HUGE under-exposure situation that you'd generally try to avoid. You'd have to be asleep at the wheel, or a Nikon shooter, to get the exposure that wrong. Still, you can see the difference the new sensor makes.
Set the 5D4 and the 5DS R to 0EV and compare the hair detail in the brush and the properly exposed 5DS R image blows away the 5D4 image in terms of detail resolution. I'm not ready to give up that detail by underexposing.
Time for a 5DS R II.
Dave