What do you shoot? Birds? You might find the 500 f4 'better.
If you read lots in this forum recently, you'll see strong praise for the 500 f4 e fl in posts lately. I'm impressed with it, although I probably prefer the creamy bokeh of the 400 2.8 e fl more, and I try to position myself in relation to my subjects such that I can use the 400 2.8 the most, although the stupidly expensive Nikon 120-300 f/2.8 lens is my most used.
I also have the also stupidly expensive 180-400 f4 TC lens, which replaced one of the 3 copies of the 200-400 f4 lens that I've owned over the years (I sold the first one because I got poor for a while), and the second copy I got used was SO out of whack, that an auto focus fine tune of 20 still wouldn't give me in focus images - not on 5 camera bodies.)
The zoom range of 200-400 f4 is really nice, and very useful for many people (sports, some wildlife), and the added range of the 180-400 f4 with built in TC gives you up to 560mm at f/5.6 when you engage the built-in teleconverter, but my copy was very disappointing with the TC engaged, and if I had only one lens that I could ever use, it might be the 180-400 - but after I became disenchanted with that lens, I bought the tragically unknown 120-300 2.8 (which is rated better by Brad Hill than the 180-400), but then I needed something longer in a two camera setup, so I bought the 500 f/5.6 pf to add to the 120-300 - but that lens needs to be put away SO much sooner at sundown than the f/2.8 lens. The difference between f 5.6 and f 2.8 at sunset is huge.
So then I wanted the highly rated newest (F-mount) version of the 400 2.8, and it had to be the e fl, because I shoot handheld, and the other versions of that lens are SO much heavier - but I couldn't believe how hard that lens was to find.
And then I got lucky on a very good deal on the Nikon 500 f4 e fl. And I was planning on adding a Nikon 600 f4 e fl to package, until the new mirrorless 400 2.8 TC Z lens was announced, and I planned to get that lens to go with my Z9, BUT, I'm disappointed in the ability of the Z9 to get they eyes of my puppies in focus, as well as my D6 or D5 does.
So now I'm back planning to get the 600 f4 e fl as my next lens - but taking 4 big lenses out on 4 cameras at once is a MAJOR logistical nightmare. I actually bought a $6,000 plus tax (Canadian) ebike that converts into a stroller at the flip of a switch to take 4 big lenses and 4 cameras and my puppies out to the park - but haven't used it yet. :-(
And all 4 of those lenses are required to replace the 180-400 f4 TC lens, because I just find it useless beyond 400mm, with the TC engaged, although some people find the drop in sharpness acceptable when the TC is turned on - but others agree with me. Several people that started with that lens have moved on from it, including Brad Hill, I believe, maybe Steve Perry too (I'm not sure about that).
