I decided to shoot a quick series of pictures at ISO 6400 and 12800 to compare the 1D4 and the 5D3. I don't tend to shoot small collections of nick-nacks like DPreview, so I shot my near comotose daughter who was watching TV.
I'm going to bang these out in three quick sets so you can view them side by side. I'd say functionall the 5D3 and 1D4 are very close, which suits my needs as I tend to shoot at ISO 6400 to 12800 a lot.
I'll start with ISO 6400 and zero NR. There is some input sharpening of 50/0.9 applied and no output sharpening.