I use mk3 and 1DX2, the mk3 maybe the tiniest bit sharper but you'd be looking for the 2mp difference in the two, perhaps at max zoom in LR and ideal conditions you may see the advantage if you study them hard enough, if I am honest I think I have seen slightly sharper images from the mk3 BUT the conditions have to be perfect, unless you shoot under studio conditions I think that's rare, the 1DX2 beats the mk3 big time in all other ways! So much so the mk3 feels dated compared to the 1DX2, it gets worse depending on what lens, for example from min to max FD the mk3 doesn't even focus with the 500/4, it does but you need to manually focus 80% of the way before the 5D3 picks up and locks on, the 1DX2 snaps to the subject from one end to the other, if your shooting close and want to follow a subject as it moves away the mk3 is not so bad but the 1DX2 is mind blowing AF wise even at 700/5.6! Also noise is an issue for me with the 5D3, the 1DX2 has noise much higher up but it cleans up nice, where the 5D3 cleans up lower down images always look soft. As for speed and shutter lag, well, as I say the 1DX2 is mind blowing, also video is superb on the 1DX2, I am not even sure why they would compare them tbh. Having now read the DPr review I feel its STILL bias to the Nikon, I used the D5 for a day and feel completely the opposite to the review! I love the way DPr seem to always be able to talk down the Canon whereas they never highlight the downsides of Sony and Nikon, perhaps the pay off still sways the other way..