The DR is technically decent (not Exmor-like, but decent), but the darkest few stops are so badly affected by pattern noise that they're essentially unusable, especially if you need to do any sort of processing to bring out the shadows.
I'd say the functional DR is 3-4 stops less than the measured DR due to this pattern noise. The 6D has a similar measured DR, but the lack of pattern noise means that the usable DR is much greater.
Both cameras, though, are sorely lacking resolution for making large, detailed prints. 20/22MP was good for 2008, but inadequate for 2014.
How large do you print ? The max size I can print at home is 13x19 and they are incredible. I don't think that throwing 35-40 MP is necessary. (for me anyway)
About DR, I don't see the big deal...I expose to the right and bring it back down in post. The shadows slider also works really well...perhaps this step is not needed with the D810...