What you really want to do is to shoot arrows that have been tuned for your bow. If you were shooting 520 grain arrows that were tuned for your bow, and you just drop 20 grains point weight and start shooting 500 grain arrows, you will find that they are a little stiff for your bow. On the other hand, if you've never tuned your arrows for your bow, you might not notice much difference.
For hunting, 10 gpp is fine as you probably won't be taking shots beyond 30 yards, and there isn't much arrow drop at that distance. If you're shooting 3D at 50 yards, you would notice quite a difference in the point of impact between 8 gpp and 10 gpp arrows.