Get a 1DX. Seriously. I print all of my photos in sports to 8 x 10 or better and the quality will make your heart melt. The detail is stunning despite 18mp vs. 22mp on the 5D3. I like the prints from the 1DX much better than any camera I've ever owned. You won't be disappointed.
And after I sell EVERYTHING to get the 1Dx what lens would I use? I'm beginning to lean to the 5D MKiii based off of price, and selling my current 5D and 70-200mm
First time I got my EOS-1vHS, the wow factor was tremendous with that sexy body and the shutter that just went OFF like a roadrunner. After a long while, now I use 5D III, which may not have as much wow factor, but after trying a grip, I actually prefer the 5D III body without the grip for the less weight and more portability. And if I really think sanely, 5D III does everything I need it to do. The small body/sensor differences among 5D III, 1DX, even Nikon D800, etc are simply not that earth-shattering when lighting/strobist and lenses make so much more impact. I'd rather spend the money on better lighting setups, triggers, and lenses..