either one will probably work, depending how long you leave them,,,I usually leave mine a bit long and so the heavier spine works,,,, if I need to tune them I can cut them a bit shorter,,,, I have so many arrows,, I can usually try a few out and see what works before I buy some for a bow,, ok I know thats no very clear,,,, try the heavier spine,, cut them a bit long and shorten to tune,,