I recently rented a Nikon Z7ii (with battery grip), Nikon Z 400 f4.5 S lens, Nikon Z 2x teleconverter. This is my experience.
After two decades with Canon (film, then 5Dii,iii,iv), I switched to Nikon D850. I now own two along with a variation of the so-called lens trinity: Tamron 15-30 f2.8 G2, Nikon 24-70 f2.8E, Nikon 70-200 f2.8E, plus 1.4xiii teleconverter.
LONG LENS ISSUES
My dilemma has been finding a long lens for wildlife. My local dealer was able to get me a Nikon 500 f5.6 PF much faster than any of the big dealers. It worked well, even with 1.4x teleconverter, but I found I wanted a zoom.
I rented and then purchased a Sony A74 (with battery grip) and Sony FE 200-600 lens along with Sony FE 1.4x teleconverter. It is amazingly sharp and well-built (the lens, not so much the camera). I used it for one year and just traded it in because I found it a bit heavy for a walkaround lens. I also never loved the electronic viewfinder, and even renting a higher resolution viewfinder A7r5 seemed about the same.
NIKON Z7ii TEST
The viewfinder of the Z7ii did appear crisper than the Sony (both of which were superior to a Canon R5 that I was able to try briefly on two occasions). The battery grip seems to be a more snug fit (no wobble) than the Sony grip I had. Holding it vertically felt quite nice, but holding it horizontally made my big hands feel a bit scrunched in the grip that is not quite deep enough. Sony made the grip on their recent models deeper after users complained and Nikon should do the same. The placement of function buttons next to the lens barrel means my fingers hit them inadvertently.
The one deal breaker IMO for wildlife shooters is the lag on startup. When the camera goes to sleep mode it takes what seems about two seconds to start up after hitting the shutter. If you only shoot landscape or architecture this won’t matter, but for wildlife two seconds can be an eternity. For example, I missed most of a coyote walking across a wash while waiting for the camera to wake up. Neither of the two Sony bodies I used had this issue.
NIKON Z 400 f4.5 S TEST
The lens is stellar and may be the perfect telephoto if you don’t need a zoom. (After using it I was reminded that I do need a zoom). Nikon has nailed it with a perfect balance of compact size, sharpness, and relatively large aperture. You can’t get f2.8 unless you are rich and a body-builder (or only shoot from a hide or vehicle), but most people can carry this lens and get 2/3 stop faster aperture compared to an f5.6 zoom. One oddity is that it has Vibration Reduction but no switch on the lens to turn it off (done in camera menu).
NIKON Z 2x TELECONVERTER
My own experience with teleconverters for SLR cameras reflects the general consensus. That is that 1.4x teleconverters can be useful but 2x teleconverters are not sharp enough (plus they don’t autofocus with “slower” lenses). Reports are that mirrorless 2x teleconverters are much sharper (and autofocus with any lens designed to accept them). I only tested it once, on a stationary acorn woodpecker, but it seems almost as sharp as the bare lens to me. The overall test (even without the converter) may be flawed by the fact I forgot to rent an Arca Swiss plate for my tripod and had to shoot these handheld in low light (braced against a post). But based on this I would feel comfortable using the 2x teleconverter for Z system. (All samples are camera JPEG’s).
When switching back and forth between my Nikon D850 and either the Z7ii or Sony A74, I find the D850 is much more enjoyable. There is no compelling reason for me to switch to mirrorless, even if I could afford another system swap (which I can’t). I ended up getting the venerable Nikon 80-400 f4.5-5.6 VR a week ago, which meets my needs well. For the type of shooting I do, being able to zoom as wide as 80mm (vs 200mm) is more useful than being able to zoom out to 600mm (vs 400mm). I post my experience in the hope it will help someone else.