Rob, unfortunately I killed my D750. Loved the camera. I replaced it with the Sony a7iii. I can do pretty much everything with the Sony that I could do with the D750 but I've never bought any long lenses for Sony since I have a good, but dated, collection of long glass for Nikon. Enter the Z6/7. I actually bought the Z6 for my long Nikon lenses. Buying the Z6, FTZ and 24-70 f4 kit was appreciably cheaper than the Sony 100-400. I still have D500, Df and D300s. The Z6 is not the best for Sports and BIF. I prefer the D500, Sony a7iii and Df. In that order. Part of it is OVF for me is better for fast action which can come from any direction. The a7iii and Z6 still have some quirks associated with the EVF.
I have had to take a hard look at what I am shooting now. For several reasons I do not shoot as much Soccer these days and the Birding in Goa has really gone downhill. Loss of habitat and changing weather patterns.
These days I shoot mostly Events, Street, Documentary and some promotional stuff. I pick up the Z6 most often these days. It gets the nod over the a7iii due to the user interface.
I pretty much agree with Paco. Battery life has not been a problem for me. The 58 1.4G still resides on the Df as does the DC105 f2D and 85 1.4D. The 58 1.4 works well on the FTZ.
I have no complaints , for my use, with the Z6.
Cheers,
Edit: the Df may go and maybe not
If I am out just for photography I take at least two cameras. I always have a camera with me when I leave the houe and that camera tends to be the 6.