In these harsh conditions, both camera's photos are equally awful and I don't see any enhanced performance of one or the other. At least with minimal processing I can't. I don't think the determing factor for any sane person is going to be high ISO or IQ differences, because they just don't exist. Speed, shutter durability, AF-point linked spot metering = 1DX. High MP, high ISO, price = 5D Mark III.
I just am not going to find anything. I mean, we can argue that the shadows are cleaner on the 1DX or we can pull more detail out of the 5D3's shadows, etc., but it's not significant enough. The last test will have to be low ISO's, where we saw more green hueing in the shadow areas when people, on a sunny day, were standing in the shade, on the 5D Mark III. I want to see if the 1DX does this or not.