Wanted to say I made it back last week from three great weeks traveling through the Middle East. Thanks, everyone, for all your suggestions.
I wound up taking nearly 9000 photos, and, yes, I really carried my full pack with me almost all the time. About the only time I didn't was in the tight confines of tunnels under some of the pyramids, though even there I carried two bodies with zooms, one wide and one long.
I'll admit, a few times I ached at the end of the day, but I'm not sure I would have done it any differently. I wound up using just about every piece of gear I'd brought along, the only exception being the 7D I'd carried as backup in case one my bodies failed.
By the way, that 1DX totally rocks; it's just amazing the quality of images I was able to get in almost no light.
I'm still recovering from jet lag, but I'll post pictures in the coming days.