My only data point on lens comparison is the 50mm 1.4 that I own for each of these cameras. I prefer the Canon lens... so far. I know that the Canon focus' closer, but I don't know that it is sharper. it appears so in the ground glass, but that could simply be an artifact of the GG itself. Another question: Does the Nikon focus screen transmit a less sharp image from the lens than the Canon focus screen? I don't know. Ultimately, I will need to set up a focus target and then expose the same film type through each camera where the subject is the focus target. The human variable in this test is my own eye. Can I focus perfectly?
I can pick up a Canon 105 or 85mm equivalent to my Nikon lenses of the same focal length and add another point to my dataset. Has anyone else got both Canon and Nikon lenses in the same focal length? I know that Nikon has a reputation of making better glass, but is that borne out by actual APUG user experience?
Another variable is the relationship between lens/mirror/screen and lens/filmplane. If this isn't spot on you'll be testing nothing.