I don't know, what is your reason for feeling the need of an upgrade (or change).
I would look into this:
- last Leica pre ASPH 90 Cron (less than the latest 90 Elmarit-M, one stop more for the needy, very nice for portraits, fantastic build with sufficient integrated lens hood)
- Canon 100/2 LTM (this is a crazy lens, that really caught me by surprise - super sharp and contrasty for it's vintage from f2 on (!), so maybe not the first selection for your models beauty shots, long focus throw though, as not a tele focus design, but a nice, light built, similar in weight, but longer than the latest 90 Cron pre ASPH).
These two are really different lenses to the one, you ask about upgrading, both entirely different in imaging, both faster than yours (do you want/ need that), both much less costly than the 90 Summarit (I see no reason, ever, to buy a 90 Summarit, when such excellent 90mm lenses are less expensive second hand).