I own both cameras and in my daily usages I've found the AF performance to be very similar with the 1DX having a what seems like only a slight edge.
Where the 1DX shines for me is in the low noise of the files that come out of it. Simply amazing camera in low light situations and clearly superior to my 5DMkIII. I often shoot at ISO 10,000 with my 1DX but won't go above 6,400 on my 5DMkIII (just personal taste). Other than that, they seem to lock focus about the same, so if AF is your only concern, I'm not sure the 1DX's price is justifiable for your needs. However if you care about low noise and super fast fps e.g. shooting sports etc... indoors, then the 1DX is your camera.