I am no technical expert, but I ride a Trek 5200 47 cm WSD with 650 wheels (the "old" version of the Madone). I love my bike. I am 5 foot 1. This summer I went on a bike trip with Trek travel and rode a Madone 47 cm with 700 wheels. I don't know how they fit the bigger wheels on such a small bike, but I hated it. The whole bike felt different; I felt like I was up on a higher bike and generally it took me a while to get used to it. I noticed no difference in my speed, but a lot in the handling. I don't race, but if i were you, I would buy the bike that fits. Most people will tell you not to get the 650 wheels, but they don't know what it's like to be short!