I traded in my 5Diii for a 1DX. I also own the 7 Dii. If I could swing it I would have two 1DXs. The 1Dx is better for even birds. I read others saying that and did not believe it. It's true. Better images cropped in and more keepers than 7Dii. Same with sports. 6d, 7dii and 5diii are all great, nothing wrong with any of them, that is why it is a tough descision and long thread.
Get the 1DX other wise you will be second guessing because you don't have the top camera. Best being relative. The new 5Ds for landscape seems killer too

The 1Dx is the fastest-acting camera already released by Canon. It certainly has a benefit there, and the larger sensor gives you more jump room to get whole birds where you might lose the head with a 7D2. Perhaps the AF is a little better, too. However, you can't get the detail of the bird that you can with the 7D2, when you do get it (and it's not hard to do with the right lens). If you use a TC or 1.4x more TC to get the details with a 1Dx, you lose its potential IQ benefit by using double the ISO. You run into a wall with the f-number and PDAF quicker than with a 7D2. The 1Dx is not the super-camera.; it is better at some things and worst at getting real detail than the 7D2. Sharp pixels at 100%, BTW, is not detail about the subject; it is detail about the pixels. As soon as you upsample it to match 7D2 subject size on screen, that acuity is gone unless you pixelate it with nearest neighbor.




