what works for one may not work for another... body proportions, fitness & flexibility, riding style, position preference and differences in frame geometry all come into play...
but... I am similar in size to you (5'6" and 31.5" inseam) and I can make frames between 49ish and 52ish work with fairly standard length and rise stems. My current road bike is a Scott CR1 Pro size XS. It's 49cm, and I'm running a 120mm, -6deg rise stem. I have two spacers under the bars right now, so I have the option to drop the bars a little, which I'm considering doing, but overall the fit is good. My bf's bike is a 52 with a 100mm stem and a bit less drop and I'm comfortable on that too, and my commuting/all around bike is a Bianchi Axis 52cm with a 90mm stem with significantly more rise than the other two bikes, and it's super duper comfortable -- I could spend all day on it.
Some people my size ride bigger bikes though, I think.