Do you ever raise exposure or shadows in post? If you do you will notice a dramatic difference in the files even at low iso.
Do you ever feel the AF such as it is in the 6D II ever lets you down? If so the 5D IV will do so noticeably less often.
Do you ever wish you could crop a bit more? If so the 5D MkIV will enable that.
If you shoot jpeg and don't care for AF and don't crop that much then stick with the 6D, for everything else the sum of the specs doesn't give the true picture of how good the 5D MkIV is, for anybody sticking with DSLR"s it is a superb bargain and fantastic tool.
Well, those are all good considerations and worth thinking about. I have no doubt that the 5D IV is a demonstrably better camera and an amazing bargain at current prices. And I really do appreciate your addressing these things.
I always shoot Raw. I don't recall ever shooting a JPEG straight out of that camera. I definitely play with the exposure in ACR. But to be honest, I really haven't run into a situation where I was raising the shadows to a point where I thought noise was a problem. I'm not trying to be a smart ass, but I do try to get the exposure right in the first place and then tweak from there. It is rare that I move the Exposure slider as far as +1. I'm usually pulling the Black slider to the left just before it clips, and I slide the Shadow slider to the right for sort of a fill-in flash or reflector look, not to bring out the cobwebs in dark corners. If I need a huge dynamic range, I will bracket and let ACR do some HDR. But that is most likely to happen when I'm traveling and shooting my G5X II. For example, in a dark cathedral, I want to show detail in the dark interior, but I also want the stained glass windows to look good. I take two shots, exposing as best I can for each. I doubt that even the 5D IV can handle that in one shot, but anyway, it would probably be back in North America when I'm in Europe. Similarly, I have shot backlit landscapes out west near sunset. I wanted the clouds to look good and richly colored but still have detail in the rock formations in the dark. I had the G7X II then, and the brackets worked great. Maybe a camera could have handled that much variation in post from one shot, and I would certainly be impressed.
I haven't noticed any AF problems with the 6D II. I do focus manually in tricky situations, such as a bird with limbs all around it, and of course with macros and tilt-shift lenses. Squares light up around whatever the camera thinks is in focus either way.
Situations where a few more megapixels would make a difference are rare. There again, I try to use the right lens and get the composition close to what I want in the camera. (I'm an old guy. I used to shoot color slides.) I print things on 13" x 19" paper if I want to frame them, so I rarely need anything over 22 Mpx once cropped. When I shoot the moon at 400mm, then I crop a lot, and comparably when I shot the solar eclipse with the T3i and 300mm. The latter printed fine on 8.5" x 11" paper, and the moon shots are just posted on the internet.
Maybe I'm just not that particular, but I think I'm reporting my experiences and shooting styles more than making excuses for not buying a great camera at a really good price. And now that I think about the tilty screen, I'd still be shooting a lot with the 6D2 anyway.
My retirement funds have pretty well recovered from their March 23 low, at least for now, and if I overspend a bit, I have plenty of credit and interest rates are very low. Plus I'm not spending money on airfare, hotels, cruises, or even a lot of restaurant meals. I'm also not out shooting pictures more than two miles from home for now. It's not a slam dunk decision either way, and I don't need to be in any rush to make it. I appreciate your taking time to help me decide.