If the difference between the 18 mp 1d X and the 5d 3 is nothing, why didn't they keep the 5d3 at 18 also? I'm DEF not a mp-guy, I'm just wondering. Is it to make the noise levels separate of the two?
Wasn't there something about the 5D3's horizontal resolution being 1920 * 3 which helps clean video?
So you could ask the other way around, why doesn't the 1DX have the same 22 MPs ;-)
Good point. My guess is that a few mp's have a lot to do with noise, they can't double the res and still have two stops cleaner anymore, so every mp steals away from the size of the pixels, making even a small increase of mp shows more noise.
I'll think I'll be quite happy with 18. I was very happy with 16 on the mk4. Printed 60x40 cm recently, one of each of my kids, one shot at 10 mp 1d mkIII and the other 1d mkIV at 16, they looked like they were shot at the same res.