10-12 grains per pound is fine. Alot of people prefer heavier arrows for more kenetic energy and better penetration at close (20ish yards) ranges. The heavier arrows also soak up more vibration thus making the bow quieter and also because it soaks up vibration, it is better on your bow limbs than a very light arrow. An arrow that is too light will be like dry firing your bow and can break a limb.

"Hey ya'll, watch this"