For folks that are waiting on pre-orders, I highly recommend Crutchfield. I placed my pre-order on July 5th and got my 1D X yesterday!

I was on Amazon's pre-order since May 27 and heard nothing from them. Crutchfield has a lot of reps online ready to check your order for you, as well as any questions you may have. They won't charge your credit card until the item is shipped.
As for the comparison between 1D X vs. 5D III, I had considered the 5D III while waiting on my 1D X pre-order like many people. But I considered the shutter life, FPS speed, and higher ISO capabilities and stayed with the 1D X decision. So far, I'm happy with it.