IMHO the GPI weight of an arrow is a mute point and I have no idea why they put the GPI on shafts these days.

What is the most important numer on a shaft is the spine rating if you use a shaft that is not spined right for your set up there is no way you are going to tune the bow or the arrow to each other.

I can get 500 spine arrows that according to the GPI will be enough weight to shoot out of my 60lb bow but there is no way I can tune the bow or arrow for perfect flight with both field points and broad heads because the spine of the shaft is too weak.

Forget the GPI and worry about the Spine rating and get shafts spined right for your set up.