Well, the interesting part of the test data is showing the d810 has a real ISO 50 (47) available, labelled as 64 and 32 extended.
The SNR at the new low ISO is now pushed down to .008% gray scale, a number only attained by Pentax' K5ii series at its measured ISO of 68 (80) until now. The pixel-level DR is increased to 13.67 in the d810 vs 13.59 in the K5ii
I'll keep my old d800e; at ISO 12,800 and lower, it has slightly cleaner shadows than the new d810 at all matching ISO settings. Not by much but it seems to show a slight compromise was made to the 810's sensor system to improve the measured spec in one(some) area at the expense of others.
So IMO for the D810 it's 2 steps fwd (iso 64 and 25,600) and 1 step back (increased shadow noise at ISOs 100 thru 12,800)
it does have a plethora of minor improvements tho, enough to make it an appealing upgrade option if you only have a regular d800 or lesser FF body.
i'd really like to make use of the electronic 1st curtain shutter and the better balanced mirror-shutter system for even more easily attained maximum sharpness. Other improvements. e.g. fps and AF options and better battery life, bring it a little closer to being an all-around useful camera, not just a landscape monster.