Up front, I don't own a 6DII, primarily because it offers nothing I need over my 6Dc. I got all the features of the 6DII, for 1/2 the cost, in my 80D.
That said, I've been following this thread for a bit, and feel compelled to off some words. Wisdom optional.
Debating the IQ/noise of a modern full frame SLR is right next to pointless. Nobody in their right mind gives a FFA what the raw looks like at ISO 25,600 or any other ISO for that matter. What matters is the presentation, which will most certainly be processed. Noise is not totally a product of the sensor. Several things matter more than ISO setting: Lighting, exposure, processing to name the first three. I was really surprised by how well the 6D handles crappy light. I've posted frames shot JPG at 25,600; I am happy with them. Just for giggles, I posted a shot of my kitchen taken at ISO 102,400 w/MSNR (admittedly, totally artificial shot). No visible noise IN THE FINISHED PRODUCT, not even in the shadows. If the shooter exposes properly, and processes properly, noise is not a problem for any modern SLR. I shot my 60D at 6400 with good results.
If you judge noise by either the raw file, or by 100% views, you are wasting your cameras potential. Of course my ISO 102,400 shot had noise in it. Of course 100% views at ISO 25,600 have noise in them. So what? Take a good look at a 100% crop from an ISO 800 raw photo. You'll see noise. If you limit yourself to lower ISO because of that noise, you may as well save yourself a ton of money and buy and XSi. It only goes to ISO 1600. I recently bought one for my grandson, with an 18-55, for $75. You don't need a 6D if you are shooting ISO 800/1600.