Hi Bruce
No - I don't have the 100-400 and never owned the 80-400 lenses for F-mount. I have had 70-200 f/2.8 lenses for a long time - and usually other options including 300 f/4, 200-400, 500, 600, etc. Even the 200-500 purchase was for a specific need - light weight for handholding. In my case, f/4.5 is probably the most important feature after size and optics. I can live with anything in the 300-500 range and the 400 alone covers most of that.
I probably use the 1.4 TC on the 70-200 less than 2% of the time, but I use a 1.4 on the 300 f/4 50% of the time. That tells me I really want 400mm and compact size. Given that the 500 PF is not my longest lens, it currently gets a lot less use - maybe 25% of my images at 500mm and more and likely to decrease due to the 800mm PF.
The 100-400S is a different class of lens in this category. Nikon's two 80-400's were lenses I always wanted to like, but never could find any love for them. Mechanically, they have been weak performers. They were better at long focal lengths than the 70-200's + 2x converter, but this was the only good thing I could ever claim about the optics. As a result, I've always owned and used the 200-400mm VR, and have had various times when the 70-200 was paired with it.
Maybe it was desperation to own a native Z-mount telephoto lens, but I seemed to have found some love for the 100-400. This lens is sharper than the 200-400 wide open, and is far more compact. In addition, the new zoom mechanism maintains a consistent balance, but I do not like that the lens extends when zooming, and would have paid a premium for an internal zoom...
As for the 400 f4.5, I definitely understand the appeal. In fact, if Nikon were to introduce a high performance DX body in the Z-mount (ie a D500 replacement), the 400 f/4.5 would be the perfect lens. I could imagine swapping bodies, Z9 for 400mm and Z(900?) for 600mm field of view).
My ideal lens would be the 400mm f/2.8Z w/ built in converter or 180-400 w/ built in converter... I just can't seem to find what it takes to spend >$5500 on a lens; it is for this reason that I have gravitated to the 200-400mm lenses.
I have always found that the price to performance ratio of these "classic" F-mount lenses are so good, and this makes them tough to resist. In fact, while I don't need it, I'm considering buying another one (VRII) that is $2000
bruce