Once you owned 5D III, your 7D will more likely sitting in the bag & collecting dust.
Once you owned a 1dx, the 5d3 will look like a children's toy to you. But this is comparing apples and oranges, the 5d ff range is a completely other gear range - you get nearly two 6d or three 7d1 for one 5d3. So for those who'd like to keep their (one!) camera body price well below $2k, it will remain a struggle with Canon to decide either for good af/fps or low light capability.
Show me what your 1D X can do that make my 5D III looks like a children's toy.