First of all, welcome to the forum!
I do not own a 1DX II. A few members of the forum do, and perhaps they will chime in.
What I can do is look at different tests, but also, my general understanding is that sensor improvements from the 5D3/1DX to the 5D4/1DXII were more in the base ISO range. Not necessarily >ISO 1000
Starting off with TDP, I would say the 1DX II has just a very slight advantage at ISO 3200. Really, it is just a finer grain of noise.
https://www.the-digital-picture.com/...0&ISOComp=3200
Then, over at DXOMark, the signal to noise ratio is almost identical (look under measurements). Really, the only difference they show is in DR and color sensitivity
https://www.dxomark.com/Cameras/Comp...III___1071_795
Then, on Photons to Photos, they do show a significant difference in read noise:
http://www.photonstophotos.net/Chart...0Mark%20III_14
Having owned the 5DIII and 5DIV, I do think there is an advantage, but it really isn't as much as some internet forums would have you believe. So, you may not be mistaken. There is a slight advantage for the 1DXII, but it likely would take certain circumstances and a trained eye to see it.