When using the exact same:
1. Focal length
3. Distance to target
Thanks, but I suspect most of us know about that, but just to recapitulate and not enter any mudslinging again :-p the issue at hand is:
* same focal lengths just for the sake of discussion, but the different working distance for live critters is an issue
* not the same distance to target to have the same framing (I'd like the butterfly to fill my frame, no matter the sensor size). Given the specifics of a macro lens, this might also mean the effective f-stop differs even more than at standard distances.
* not the same aperture to reach a comparable dof, resulting in an iso shift
Overall, the 1D X and 6D deliver the best quality, with the weak spot of the 6D being its viewfinder
Um, what's wrong with the 6d vf? I've never come near a 1dx, so I cannot tell the difference and what you might refer to.