I don't own, nor have I ever used the 50mm f:2.5 Skopar, but I've read a number of reports around the web and on the CVUG list (CV user's group, private, by subscription) in trying to decide whether to put it on my list of things to get. You see reports across the spectrum on this lens, and a number of comments that it lacks the sharpness or contrast of the other CV lenses. It doesn't get the universal praise of the 35 f:2.5 you already have. As always, it's hard to evaluate the judgements of people you don't know. Do a Google search and see what you come up with. Some people really like it, some are pretty disappointed. The other CV 50mm lenses get better reports on average, but of course they're larger and more expensive. The 50mm CV Heliar gets great reports, but was only sold in a limited edition as a set with a body, so you're unlikely to see one floating around cheap and alone.

Wish I had something more useful, but I saw that no one with more info had responded yet, and thought you might want something rather than nothing.