I'm 5'5". I have a 54cm Rivendell which is 'about' the right size, though I could probably be comfy on their 52cm as well (never tried one though).
No one needs more than a 1/2" of standover, technically speaking. That's about what I have on my Riv.
You ought to measure and compare your two heights from floor to pubic bone however- that's more accurate and will tell you more than overall body height.
Here's how:
http://www.rivbike.com/article/bike_..._to_measure_it