RE: weight vs spine
Apples and Oranges. As Aussie said; start with your intended head weight. Then choose the proper spine (stiffness) from the charts - based on the draw weight of your bow (you should measure this), the cam type, and the arrow length you intend to shoot. The actual weight of the finished arrow is only a function of the gpi of the particular shaft you chose. There are very light arrows with a .300 spine (very stiff), and very heavy arrows with a .500 spine (pretty soft). The weight issue ismostly a matter of balancing out trajectory vs. penetration - although some of the very slim shafts now offered can deliver both.