With 1/8000 shutter speeds ISO 50 has only niche applications all by itself.
There is only one important item here: that is the max dynamic range.
If that can be achieved at ISO 100 instead of ISO 50 that is even better.
And if the K-1 outperforms the D810 (which itself hugely outperforms the APSC level Sony A7RII in max DR) even at ISO 100 that is better than better.
I want the biggest possible max dynamic range (for shots with bright light and deep shadows).
And I want this available at a moderate ISO, since if I can only get it as ISO 50 such as in the D810 I need slower shutter speeds to get there.
Give me 15 stops of DR at ISO 100 and I am going to be a very happy user.