I’m in the same boat as you two. Want it, don’t need it.
I’m happy with my 500PF’s performance with the TC14. The 800PF essentially amounts to less cropping at the same focal length, and a bit shorter DOF. It also will surely improve AF a bit (which isn’t compelling to me), and it gives me the new Z lens features (no FTZ, control ring).
I quantify the difference between the two options by considering my maximum acceptable crop to be DX format, in which case you can call the 500PF a “1050/8”, and the 800PF a “1200/6.3”.
On the other hand, it has two significant downsides: First, it weighs 2lbs more than my 500PF and requires a specialized bag. That’s a big deal for me, as I enjoy the 500PF’s feather-weight when hiking, and using my existing bags. Second, the 800PF ties up a LOT of cash. With that cash I could get that GFX camera I’ve always wanted, or I could buy the upcoming 85/1.2 and one of the other upcoming Z tile’s. Or I could always
not spend tons of money on a camera lens.
Balancing the logistics of shooting a “big lens” again against the benefit of more pixels for very distant subjects, it’s a tough call. I shoot for my own enjoyment, and most of my own enjoyment Is simply
being outdoors, and coming home with some nice photos. Is it worth the downsides for those photos to be nicer than they are today?
As with you guys, I’ve been teetering on the edge of canceling what I like to call “my defensive pre-order”.