When I bought my, iiic it came with an uncoated collapsible Summitar which I dated back to 1938. For several years it was the only screw mount lens I had and it's a very interesting lens - almost no contrast, flares like crazy and has that 1940-50s look to it. On the IIIc, it collapses to a small package you can almost pack into any bag you're carrying with you. Ok, setting aperture is a bit of a chore, but nothing that frustrates the photographer.
I have the Summarit 1.5 as well, but not in screw mount so I've never done an A/B test vs the Summitar. Subjectively, I would say that the Summarit is a bit more modern but quite similar in look especially when wide open (soft, possibly more glowy - all compared to modern Crons/Luxes obviously).
I dont know if you like your collapsible 'cron. If I were you I'd try to get a lens that is as far away as possible from something you already have. Perhaps an uncoated Summitar is it?