I have 50/1.4 in Contax/Yashica, Canon EF and Leica M mounts. My preferred lenses, however, are much slower. For RF walkabout, the choice is Summaron 35/2.8, Elmar 50/2.8, Elmar 90/4. In low light, I improvise with braced shooting, or the nuclear option (flash). In some ways, my best low-light kit is the Nikon D300: AF @ EV 0, 3200 ASA, inbuilt flash, 17-55/2.8 Überzoom . Who needs subtlety? 🙂