I suggest riding one. If, though, you're buying online, I think you'd be better off with the 53 Iro. A buddy of mine rides a 53 Iro (I ride a 53 Kilo), and after riding my bike, he wants to get a 55 Iro frame.
The 53 Iro isn't a 53 at all. I don't know why they call it a 53cm bike if none of the measurements are 53cm.