What kind of terrain/distance are you looking at for your commute?

It might be worth your while to check out some of the folding bike threads. I'm about the same height as you and when I had a commute I was on my folder. The low stepover of the design was great not only because of my short inseam but also because I had been working through a back/hip injury that made getting on my regular bike a bit awkward.

Bonus: I could stash the bike under my desk, as my office did not provide a secure place for bicycles during the work day.