10 gpp isn't carved in stone, just a good overall weight. I have shot arrows from 45#-ish bows ranging from 350-grains to well over 600 grains with good results-475 grains should work great. The heavier ones are good for hunting, but drop more at longer ranges. If you get too light, you can risk damaging the bow. What are you making your shafts from, and what diameter are they? Different woods or even different batches of the same wood species can vary greatly in weight. Most of my arrows for mid-40's bows are 5/16" dia. Spine is more important than weight for good flight, but that can also vary wildly even within the same kind of wood. If you want lighter arrows, just experiment with one to see how it flies after you reduce it. Tapering from just behind the center to the nock end of the arrow can remove weight without changing spine too much, and can also give better flight sometimes.