Many thanks for your feedback Elsa.
I actually found that after initially a slight struggle to get focus, once I locked on using wide area and 3D I did not have a problem.
I am very impressed with the capability to adjust settings while looking at the histogram through the viewfinder.
The planes were quite a distance away with a very bright sky at around midday, and I had to reduce settings by 2 stops to reduce overexposure.
I also did not have a long lens with me and the 24-120 Z lens still did the job.
Like you, I looked at the Z9 ,but also made a call to opt for the Z8.
Regards,
Gavin