You probably have the best lens sold on that, assuming it's a Jubilette or Baldina. I have a Jubilette with Baltar triplet, which is pretty much useless at f/5.6 or wider. In theory, you can put any 50 mm lens in a compatible shutter on there, by removing the retaining ring, dropping the shutter off, and installing the other. Between rolls, obviously...

BTW, I'd recommend trying Fomapan 100 -- I like it a lot, and it's cheaper than Efke.