I am similarly between sizes. I am a little taller than you 5'7", but have very short legs for a woman (but had a hard time with men's bikes which fit fine because my hands are child sizes and breaking was difficult). Shops had a similar problem fitting me. I rode a LOT of bikes in several sizes and had the seat adjusted a bunch of different ways until I settled on the right size. It was a giant pain and no one seemed to know what was exactly right. I did end up on a 54 bike.