Not sure if this is helpful but here are some test shots with the 5D4 with a 24-70mm f/2.8 I at 50mm, f/8 and varying shutter speeds. Tripod, Large JPEGs, Custom WB. ISOs:
ISO F-stop Shutter
32000 f/8 1/20
25600 f/8 1/15
12800 f/8 1/8
6400 f/8 1/4
3200 f/8 1/2
1600 f/8 1
https://www.flickr.com/photos/jemlnlx/
https://www.flickr.com/photos/jemlnlx/
ISO F-stop Shutter
32000 f/8 1/20
25600 f/8 1/15
12800 f/8 1/8
6400 f/8 1/4
3200 f/8 1/2
1600 f/8 1
https://www.flickr.com/photos/jemlnlx/
https://www.flickr.com/photos/jemlnlx/