If you have never owned a 1 series body, go to a shop, hold the 1DX and play with it a bit...
Yes, 1DX is a outstanding camera, but it is also large, obvious, and hefty. Unless photographic needs actually exist, it really would be an overkill for most nonprofessionals. For you 5D3 probably will do 90% of what 1DX will do and you could spend the extra cash on some nice L glass.
Cheers.