I had this exact kite. It was designed to pull as much as possible, hence FAT leading edge to maximise pull, at the expense of drag and weight. It is a heavy kite that is not good at going upwind. Only good for a heavier guy on a small twintip in not too light wind. If you already have a raceboard, then the smaller edge will be MUCH better for you in my opinion. I stopped using my 17m contra when I got a race board, and sold it not too long after. My light weight fast 14m Blade Vertigo gave me better low wind since it is lighter and faster and flies better upwind.
What year North board do you have? I would rather invest in a newer race board (or a hydrofoil

) and stay with the 13m Edge.