I realize many will see things differently. My take on this issue is that I see that no matter what you choose there will be compromise. I am just getting into the z system and have sold much of my older gear to upgrade. I have the z8, the 100-400 zoom and the 400f4.5 along with both teleconverters. I am in .Bosque Del Apache and have been able to give this gear a good workout.
For me the cost and weight of the big glass makes them a non issue although I well realize you will get the sharpest and best images from these lenses. I have been using the 400 f 4.5 mostly with the 1.4tc and also with the 2x tc. I have found that surprisingly I can in fact get some decently sharp images with the 400-2x combo in spite of the bad reviews. The thing is you are shooting at f9 meaning your iso quadruples. You need good light and good technique to handhold this combination which I only do. The 600pf is no doubt better but it’s still at f9 if you want 800mm (840). So the same issue applies. I find the 400 with the 1.4tc to be quite sharp and I like having low light options you get with a 4.5f lens With decent reach. Then180-600 is more versatile but it’s a heavy beast to handhold. Then100-400 is a lovely little lens and is plenty long for bigger stuff Plus it has good close focus for insects etc. The 800pf is obviously the better choice for 800mm but for me I’m often in need of shorter reach and it’s a beast to handhold. The 600pf is on my wish list but at 5k it will be a while.
Good feed back thank you.
Its amazing the options before us, applications, range of tools available, DSLR, Mirror less, new generation of lenses, stills on the slide, video on the rise.................amazing period in evolution.
Despite all, the fundamentals are for me.
a) enjoy what i am doing
b) select the right tools for what i want to achieve, be it buy them or rent them.
c) use the right tools for the purpose they have been designed for.
Above all remember things may be new and technically advanced, the end results comes still largely from only time light and speed in the right combination.
Light small is awesome, but gee if F2.8 or F4 primes deliver is it worth the compromise of weight and size, i mean the DSLR glass cost is super cheap at the moment.
Nikon has a great selection of glass to choose from.
Only an opinion