3Weight... I can't imagine you would ride a small frame you are taller than me! Problem with the medium frame, as I discovered with my two bikes is not they can run alittle small and alittle large.

Bottom line you need to get a good fitting and be measured and then you adn the LBS need to compare top tube lengths to see what fits you both. Unless you have ungodly short arms (think T-Rex), the small frame will most likely be too small.