I knew I was on the cusp of needing a stiffer spine for my given set up. I have been shooting full length ICS 400s with 100gr inserts and 150gr points from a Grizzly rated 45# @ 28". My draw is 30". I also use weight tubes to add 3gr/inch to the arrow as I want the heavier arrow to retain energy. I noticed that unless my release was perfect I would get a little wag. Having a few other bows with lighter draw weight to use with the 400s, I buillt up some ICS 340s with the same components. They fly like darts and accuracy is more repeatable. Consequently, the bow is quieter to boot!
Tinkering and tuning is half the fun, until I stick one into a deer one of these days.