I am considering buying a Scott Sub 20 but struggling to decide which frame size ie S v M. The problem is that the recommendation is a Small frame. Looking at the dimesions ie virtual top tube and down tube, these are smaller than a GT Aggressor that I already have. Does anyone have any experience on the frame size and in particular the Sub 20. I am 5' 7" and 29" inside leg and would appreciate any comments or experiences that you may have.