I've made the switch from a 5Dmk3 to the a7 II. I will eventually get the a7R II but will wait a while for the price to drop. I had your favorite lens, the 70-200/2.8 II and sold it for the 70-200/4 FE lens for the sony system. I don't want to deal w/ adapted lenses and I have been very happy w/ the decision. It is quite a gem in my bag. The only other lens I have is the 24-70/4 FE Zies lens and I love this guy too.
On a recent trip hiking I tested out the weather sealing, not by choice but it happened. The rain was coming down and the camera and 24-70 were completely soaked and I was using the tilt screen. I was very nervous about it all. When we got back to car I towel dried everything to the best of my ability and then when we got back to the cabin I used a hair dryer on low heat to dry it out the rest of the way. No issues to date and it's now in China with me.