I went back and did some test riding with the owner. We decided the 51 was the best choice for me. Tried the 48, but it was just too small. Went to another LBS again just to see what their opinion was and they felt the 48 would be too small as well. Tried Men's bikes but I have a very short torso so that did not work well for me either. I ended up buying the Cannondale Synapse 6. First ride tomorrow morning! Thanks for the great advice! I'm guessing I will have many more questions!