Been offered a Cannondale R500 for my son, its a 47cm maybe 48cm, just wonder what the geo is size wise. Tried him on a Triban 54cm and it was fine plenty room for growth. He fits my langster 56 but is stretched out imo too far and the seat is slammed so obviously a bit big. However before I waste my time and the sellers I was hoping to see rough sizes so can compare ?