If you need to ask I say 5D4. I bought a 1D2n new. Loved it. It's still working (as advised by it's more recent owner). I bought a 1D4 when it was about 12 months old. Loved it and still do. For many of the photos I take an 80D would result in better photos. (Birds, most often used ISO is 400. The shadow recovery of the 80D is the main reason I would say better results). With my 100-400 II lens the 80D provides 27 AF points with a 1.4 III TC vs the centre point with 4 assist of the 1D4, which is the same situation with my 7D2. I shoot a lot and my 7D2 has about 45K actuations. By the time I either sell or relegate to back up use the 7D2 will most likely still work fine and get a larger percentage of the new price back if I decide to sell, compared to 1D2n, by a large margin.
I also have a 1DS2 which I use still. I bought that in 2012 for $900, the owner paid $14k (Australian dollars) in 2004. If it dies tomorrow I have got good value but chances are it will give me a few years yet. I take risks with it, bad weather, sunsets (with the complete sun in frame) etc.
All this has made me decide that while 1s are great, their value is realised by pros who put many more actuations on them sooner and rely on their ruggedness. At this moment, 80D, 7D2 and 5D4 offer a lot of value. 1 DX2 is almost double the cost of 2 5D4s. Unless the slightly superior AF or FPS of the 1DX2 is a critical need, FPS more so than AF, 5D4 is a smarter choice.