I say the 55 is tooo small. I'm same height as you and the 57 is perfect.
55 is too small and this is why. The fork is a straight blade fork. On the 57 my toe will slightly touch the tire on a very slow turn or a track stand. Scared me at first as I didn't realize that this wold happen. Now that I know about it, it is no problem and haven't touched again. IS different from my Cannondale with rake in the fork (58 cm frame).
I will bet that if you go with the 55 your toe will overlap with the front tire on a slow turn or track stand!