I guaranty you that I could blow up a bunch of photographs to 8x10 from various 35mm cameras using the same film and you wouldn't be able to tell me which camera shot which photograph. Yes, there are subtle differences in 35mm lenses but it's not as dramatic as some make it out to be. This is all coming from someone who shot Contax and owned 5 Zeiss lenses.
I've never tested older film lenses on digital cameras.
8x10 darkroom prints from different lenses this is what I do every over week for about three years now. Usually I'm using lens for several months and printing from differently taken negatives, never test charts. And this is what forces me to Leica lenses in addition to their specific handling, which I finding to be best for me.
I have printed from Cosina made lenses, FSU, Olympus, Leica and P&S... These days it is not so easy to get old Leitz lens in condition suitable for good prints. And modern Leica lenses are too expensive to justify paying insane price for good quality prints.
I also tried older film SLR lenses on Canon DLSR and it never left me impressed. But on digital Leica it is different. I have tested old film RF lenses, FSU and Leitz. Surprisingly they are not worst to modern RF lenses. And not only Leitz made.
But to me character of the lens is more visible on darkroom prints, not in the files from digital cameras. And 8x10 paper size seems to be optimum to unveil it.
...Because since when did a great photo require great optics?
This is the question I'm asking myself every time I lith print from negatives taken by Summarit-M 35 2.5