I'm a first time poster and relatively new to biking having started about 5 months ago. I am currently riding an older Trek road bike that was given to me and is a 58cm frame which I know is too big for me. I am considering buying a new road bike (Motobecane Le Champion SL). From all I have read and also from having been measured at two local bike shops it seems the ideal frame size for me would be 55cm which of course is not offered. Would it be better to go up to a 56cm or go down to a 54cm? Help!!