Also I meant to add. Be sure you have plenty of fletch on your arrow. For bows 50lbs and up I wouldn't shoot anything less than feathers 6 inches. When you use this size fletch on your arrows, spine becomes less critical. If someone doesn't believe this take three shafts of the same spine and fletch one with four inch, the next with 5 inch and the third with 6 inch, all parabolic shape. See for yourself which one shoots best. If you have plenty of fletch on the rear of the arrow, it will straighten up quicker coming out of the bow and cause spine to be less critical. Don't worry about the speed factor, accuracy is of the most importance.if it is speed your after, shoot a broom straw through a chronograph. I promise your bow will be the fastest it can possibly be.JERRY HILL.....