I think TMF Syndrome (Too Many Fifties) is so widespread that the American Psychiatric Association DSM should probably have a section on it. 😉 My own case has been severe and prolonged. The problem is that there are so many different 50mm lenses available, and many of them are reasonably priced -- how's a gear-head supposed to resist? :bang:
My current stable for the R-D1 (my only Leica mount camera), which is long overdue for reduction, consists of:
Canon: f/1.2, f/1.5, f/1.8, f/3.5 collapsible
Nikkor: f/1.4, f/2
Leica: f/2 Summicron Rigid, f/2.8 Elmar collapsible (1960s M mount)
CV: f/1.5 Nokton, f/2.5 Skopar
(Amazingly, I was able to bring myself to sell the Konica M-Hexanon 50/1.2 Limited, which was just too big for my tastes.)
That makes 10 fifties, 3 of which are Sonnar types and 2 of which are Tessar types. Obviously, I don't need that many for any reason, whether different lighting conditions, compactness requirements, etc.
The ones I use most frequently these days are (in descending order) the Summicron, Nokton, Nikkor f/1.4 and Elmar -- which do, in fact give me a variety of different looks, contrast ranges, sizes and max apertures for different situations. The rest I could probably sell without impacting anything but my lust for fine lenses.
The foregoing notwithstanding, my most-used focal length on the R-D1 is 35mm -- of which I have a few too many as well. 😱
Long story short: Your Sonnar and Elmar give you a nice range of options with top-class quality and distinctive signatures. If budget is not an overpowering factor, you shouldn't feel too bad about keeping both.
::Ari