Well, let me be honest. The 5D Mark III is a great camera. I own one and use it all the time. But if you're doing weddings, the 1DX is actually better, and if you're doing sports, the 1DX is still better. The sensor tech is better. If you routinely shoot in difficult situations where you must recover highlight detail or shadow recovery, the 1DX files are much better in that regard. Not to mention AF, which is better in the 1DX as well.
Can you shoot weddings and sports with a 5D Mark III? Of course! It'll do the job just fine, and actually will be a huge upgrade for you. Just because the 1DX is better, doesn't mean the 5D Mark III isn't absolutely fantastic. My roomate was a 4:00 miler. Jeff, our friend at OSU, ran 3:53. Didn't make my roomate slow did it?