you will get a lot of good answers from a lot of people, but i firmly believe that the center cut of your bow will be what determines the spine that your particular bow likes. when you get close on spine selection, there are ways to fine tune the dynamic spine from there: shaft length, point/insert weight, building out your side plate and believe it or not string silencers. i was bare shafting my latest longbow, and went from a weak spine to a stiff spine with the same arrow just by adding beaver ball silencers, and now i will move the silencers closer to the limb tips to weaken the spine a little more, if that don't weaken the spine enough, i will put on lighter silencers. i actually find this tuning stuff kind of fun.