I've hit the same dilemma as you, John, after Canon have thrown the curveball of making the 5D III significantly better than I was anticipating. Naturally I have both on pre-order for now, and have at least a month (probably a bit longer ) to decide which to cancel. To be honest, either camera will meet my needs. It's a body that will likely stay with you/me for 3 - 4 years, which is currently leaning me toward the 1D X at the moment.
Something that is a minor annoyance but worth putting into the table... no compatibility with the inexpensive infrared remote for the 1D X. Something I use more than occasionally for family shots and also macro work.