Honestly, I would go and get fit for a shaft (if you can afford it). There is so many shafts out there, it is hard to say. Choosing a shafts should be based on launch, spin, and trajectory numbers along with feel. The stock shafts that come with the 913 are actually not too bad. I can give you a little advice for high school golf ( I am almost done with my junior year). Hitting fairways is very important. The fairway gives you a chance to be aggressive with the next shot so you can still post good scores, but the less pressure from a recovery shot in the woods is on you, the better you will play. If you are playing an 8.5 degree driver, then I guess you have a pretty level impact or you are striking the ball on the upswing. I would go with a moderate flexing shaft (not super boardy or super whippy) My recommendation would be a Fuijikura Motore f3 or speeder. The stock shafts on the 913 work well too. I would go with a stiff shaft for consistency. I'm also not sure what the difference is for an exotic shaft, but it is definitely more. 

Hope this helps and good luck