Here’s a followup. I shot Basketball this evening, and during warmup I shot some in the same environment with the D4 and D5, between 3200 and 25,600.
I processed these in Lightroom with the same default preset I use, no special approach to the higher ISO. They are also a tad bright I think in a few cases, but I did not adjust exposure as I did not want to bias the ISO results.
I’m going to stick with my “underwhelmed” answer, with regard to ISO. There’s a lot to like (I’ll try to post a followup on focusing, which I am still pretty enamored with, later).
PS. Oh, wait… you wanted to know which was which? Can’t you tell? The D5 was on the left.