I currently alternate between the 100-400z and the 500 PF on my z9. I am using the 500pf with the 1.4 teleconverter, 90% of the time. I also use the 1.4z on the 100-400 on occasion. After months of use, l still prefer the images produced by the 500pf, when compared to the 100-400, even with the teleconverter. So, the majority of use of this lens is at 700mm. The limitation being the maximum aperture of f8. A few months ago, I decided to order the new 800mm, which of course I am still waiting on. Originally I had intended to sell the 500 when the 800 arrived. However, I’m starting to have second thoughts about the 800. I absolately love the 500, 1.4 combination. I know having the 2 lenses in hand will help me make may decision but i would be interested to hear from those 500pf owners that recently acquired the new 800pf 6.3. Do you have one that you prefer more than the other?