I have zero 1DX experience, so I can only give a 50% opinion.
I have a 1D4 and a 5D3. The 1D4 is better between them for sports, mainly because I think it drives AF motors faster and the burst speed / lag time is better.
I do not doubt the 1DX is great, but it is a lot of money. If you are looking at high ISO noise, what I can tell you is the 1D4 and 5D3 are about on par. I'll use either up to ISO 12800 for large prints, and no higher. I don't know if the 1DX from RAW is capable of better.
Get the f2.8 lens and 1dmk4 if 7d still doesn't cut it.
