There are times when stars are aligned... That was last Chrismass vacation period when my Pro rep offered me a $500 discount on a brand new 5D MK IV. And after heighteen months working with the A7R II for landscape photography, I was considering it's limitations and issues: the identified zone in focus which is not quite right, a very poor battery life which has been a problem in Iceland last September even though I had 4 batteries and 2 chargers, the lack of joystick to choose the focus points, the loosening Metabones IV in colder conditions (below 60F) and the weird yellish/greenish and strange sky colors in certain situations to name a few.
If I was rich, I would have maybe kept the A7R II as a backup for landscape photography, but the colors were still a problem for me and I am not rich...
I have been using the 5D IV for nearly 4 months now. No, it does not have 42mpix, but 30 are plenty to print big. There are a lot of details in the files, colors are perfect, and I am back with a great menu system, bigger LCD, superb autofocus, and 7i/s. The camera allows for rapid changes in the setups when these are needed. I love Canon colors in their Pro and Semi-Pro bodies. They are just right. The dynamic range of the files are also great and a lot better than the 5D III (almost 30%+), and the noise level at ISO 1600 and 3200 is low compared to past 5D cameras. These ISO level I use when the 5D IV is used as my wildlife backup or for anything else than landscapes. I foresee some great results with the starlights shots or moorises.
One cool thing with the camera is the the new touch screen which becomes very useful for still shots on a tripod or video when changing focused elements and seeing the focus passing from one to the other very smoothly: that is a plus. This screen is like a smart phone for many actions.
The 5D IV is proven to be a very solid, reliable and well thought camera with enhanced capabilities and it feels right in the hand and well balanced when used with super tele lenses. So far, I would not go back to the A7R II at all.
Best of life,