With the 9 degree wedge you will have 40 pieces to make the circle. With the 10 degree wedge you will have 36 pieces to make the circle. If it is a specific pattern requiring so many wedges of each design, then you will have to use the 9 degree. But if the pattern is the same for each wedge, (or just two different wedges) there should be no problem. Just cut less wedges.
I have used both of the rulers to make the spicy spiral and there was no noticeable difference. Good luck. Ann