RE: Correct arrow spine
Its better to be overspined that underspined in all instances , but when shooting fixed broadheads like you are , its even more important , never go on the weak side of spine .
Of coarse you can take this to the extreme and your groups may open up some with a target rig and field tips , with tiny fletching .
Enter your specs into bowjacksons website , and it will give you an close idea of what spine arrow you should be shooting , look for an a rated shaft for fixed broadhead equiped arrows .
Another way to adjut for spine if your arrows are too weak , is to take a turn out of the limd bolts , to lessen the weight you are pulling .