Every image has noise present. You make the point that noise does not matter when, as usual, the presentation of the photograph does not disclose the noise. Same goes for defocus. I cannot comment about the Cannon cameras since I use Nikon. Also I have never used a Nikon Df but I would expect it to have a very good noise characteristic. My present D500 cameras are also low noise. I would expect D5 to be better because the photosites are bigger and both cameras are of the same generaation. The Df photosites are also bigger but the sensor is of an ealier generation. Now back to Gary and his original question. It seems no one here has both a 7D Mk2 and also a 5D Mk3. I would expect the 5D Mk3 to be better than the 7D Mk2. Whether the difference matters depends on the size at which you present your photographs, and the low light conditions under which you carry out your most challenging photography. Gary. Can I suggest that you hire a 5D Mk3 and do some tests which are relevant to you. Also if you do so I guess that it would be very helpful to other Cannon users if you were to publish your comparisson in the user review room.