So, I had enough time to be able to get the proper confidence with the D750. Used it on the wedding I shot this past weekend. I'll have some images to share soon from that, but I wanted to give the bride and her family some time to see them before the rest of the world!
IQ is excellent. Really close to the Df in some ways. What I noticed right off the bat is the exposure "brain" is much more intelligent than the D700. It handles back lighting WAY better than the D700. I also noticed a very slight increase in AF speed and acquisition. Most people may not notice it, but I did. Would it matter in 99% of situations. Heck no!
I had the Tamron 70-200/2.8VC on it for the duration and it only had one hiccup and that, I believe was my fault. I'm not used to the body yet and my left hand wrapped around the bottom of the body and I accidentally bumped the lens release. It was just enough to have the lens stop responding. Unmounting and remounting fixed my mistake.
What I do miss when using the D750....the speed of the D500. That damn camera has so spoiled me, it is not even funny anymore. When you can rattle off 10fps at will...then going to a D750 in continuous just seems anemic. However, as mentioned previously, shooting high speed sports or 10fps is not this cameras primary role.
I do wish the D750 had a 10pin remote port. The only Nikon I have that has that port is the D500 now. I use a Vello remote trigger and the only cable I have is the one for the 10pin. I had need for a remote camera, and I needed to relegate the D500 for that. I know this is a "tough problem to have" but I then needed to use the Df with the 24-70/2.8 and the D750 was used with the long lens.
I'll have to order another Vello cable to use with the other 2.