Unfotrunately, arrows are a product where you get what you pay for. The extra $20 for arrows that have closer matched weights (+/- 1) and trueness (+/-1 .001") is money well spent. Better arrows will result in smaller groups and increased confidence. I would put a post in the tech forum with all of your bow specs and get someone to put the numbers in their software (OT2, Archer's Advantage). Sometime the spine chart are off with today's hard shooting bow. The entire weight of shaft, inserts etc is included in the IBO weight.

Start with spine. Buy the best you can afford. Shoot the same arrow for 3D.