I don't think there's a generic answer to that question. If you're taking film grain (which appears to be the point of copex, etc.) and enlarging conditions out of the equation, it depends on which Leica lens and which MF lens you're talking about. As df mentions, the newest Leica glass is amazing (I don't dare go near a 75 Summicron or a 90 apo).
Originally Posted by Troy Ammons
I offered to shoot samples with 25 year old glass, and that's obviously superceded to some degree, but maybe you should ask for test rolls on the film you want to use from APUG members with the latest Leica glass in the f.l. you want and with the MF glass you want. I'm sure a couple of folks here would be happy to oblige.