I am 5' 5 1/2 " and have an inseam of 30 1/2 ". My LBS has indicated I should be testing out a 54cm road bike. I thought I would 50cm would be my size. I have tried two Specialized Allex in both a 52 and 54 cm and both felt fine. But I have much more testing bikes to do. As I look at the geometry of TREK, Cannondale and Specialized, I apprears to me that in some cases a 54 WSD has similar geometry (top tube length) to that of a 52cm men's bike.

My advice is do not buy a bike that is too small just because it is available and a good price. I have been there and done that. My hybrid has the seat pushed the whole way back, longer stem installed, and the handlebars all the way down so I am not scrunched. I was in too much of a hurry to buy a bike, this one was availabe and appealing moneywise. Take your time, be patient, test out numberous bikes before making any rash decisions. You want to be happy for years to come not days.