I have made a final decision.. sell off my 180-600 Z and replace with Z 400 mm 4.5 and add Z800 MM PF. I go once in a year to Safari and i think i should be good . I have Z9 ,Z9 and D850 with 70-200 mm 2.8. Any thoughts?
You ask for any Thoughts...
My self i would rent each lens for a weekend and shoot at subjects be it birds cars planes trees emulating the focal distance and conditions expected on safari, its going to show you hands on what to expect, be it the good the bad or the ugly.
May i ask what is the most common focal range that you used to date on safari, how does that compare to what you felt you lost of missed out on ?
A question, what are the environmental conditions in changing lenses in the field on Safari. Is that something you do or do not want to do, the D850 would be more vulnerable to sensor dust than the Z9.
The 800mm is stunning PERIOD, it will transform your photography in general not just on safari or long range shooting in fact my friends use it more for closer shots than longer.
Such a long lens like most long lenses
adds compression to an image offering a nicer back ground.
Shooting that lens as close as possible to the subject will impress you be it a lion or even a flower only meters away.
The 400 is stunning even with a 1.4 TC.
As is the 600 PF and may work well with a TC 1.4
In good light there isn't much wrong with the 180-600 but may be far from ideal with a TC.
The 70-200 can always be in your bag, your past image focal length data analysis will determine the priority or strategy.
My self i felt the range of 100-600 was excellent focal range, but you would know more based on your location on Safari.
Only an opinion