To me Image quality is the only deciding factor (details, tonal range) and this confirmed 5D iii spec is simply not that tempting, especially after looking at the spec of Nikon D800E (it just SOUNDS like there will be more details and sharpness, needless to say bigger file size for cropping in should the bad bad photo editor / client want to,) I am in serious doubt whether I should go for the 5D iii or jump ship to the Nikon camp.
As for the disappointment that is 1Dx, just in what way is it better than the 5D iii to justify almost twice the price? I know it is bigger individual pixel size, but from the sample photos available so far, it is simply NOT impressive.