I'm a long time reader, first time poster, but I have to address Neuro here.
Welcome to the Forums. I have to say, I find your characterization of me to be rather rude and offensive. You are, of course, welcome to your own opinion...but it's unfortunate that your opinion is apparently based on comments by the likes of dilbert, rather than my own posts.
Can you find a post where I claim that Canon sensors deliver better low ISO dynamic range than Nikon/Sony sensors? No, because the opposite is true, as I've stated more times than I can count. I've also lost count of the times I've stated that if I were primarily a landscape shooter, I'd be using a D800E and 14-24/2.8G.
The issue at hand is that for you, like most people, everything is colored by your personal viewpoint and experience. For example, I say DxO's Scores are biased, but you say they back up your experience. Given your statement, "I am not a high ISO shooter," perhaps you don't see the bias inherent in their Scores...because that bias favors your shooting needs. How is that 'open minded'?
...but please, can we have some debate that actually understands what DR is...
Ok, but you'll have to excuse yourself from that debate. When you make statements like, "With over 14 stops at 100 ISO (14.8 at 32ISO on the D810 it would appear)," you demonstrate that your understanding of the relevant technical issues is quite poor. The D810 has a 14-bit ADC, it is not capable of recording over 14-stops of DR in a RAW image. DxO's 'Landscape Score' of 14.8-stops of DR results from a mathematical simulation of downsampling that 36 MP image to 8 MP. If you go out and meter a scene that shows a 15-stop difference from darkest to brightest, and take one image with your D810, you'll lose 1.25-stops of some combination of shadows/highlights, depending on your exposure. That's at low ISO...once you get above ISO 800, the D800/810 DR advantage evaporates.
I don't believe in the concept of "pure IQ" – I believe in taking pictures. A better sensor coupled with a worse lens does not make for a better picture. A sensor with 20-stops of DR coupled to a 600mm f/4 lens that I cannot handhold would not adequately meet my needs.
Everyone's needs are different. Aglet needs to shoot images (sometimes with the lens cap on) and push the files 4-5 stops in post. It's rare that I need to push an image more than 1 stop, and I don't think I've ever needed to push an image more than 2-3 stops (in those rare cases when I completely screw up the exposure).
The problem I have is when people assume their needs represent the needs of the majority, and what they find to be a limitation is universally applicable.
If the D800/810 meet your needs better than your Canon gear did, then switching was the right decision and good for you. You didn't like the 5DIII? That's fine.
The D800/810 sensors have better low ISO DR than any Canon sensor. But...people don't buy bare silicon sensors, they buy cameras. I believe the 5DIII is a better 'all around' camera, and the sales figures are consistent with that belief. More people chose to buy 5DIII's than D800/E's, just as more people have chosen Canon dSLRs over Nikon dSLRs for at least the past 10 years. That's objective reality. Does it mean Canon is 'better'? No...only that Canon is chosen by more people to better meet their needs.