Try to find an arrow in the 380 to 400 grain per inch.This is with your arrow,fletching,nock and tip added weigh.Your right though,a arrow weight of 5 grains per pound would be good start.
If you went with an arrow weight of 8 grains per inch then you would have an arrow weight of 249.Remember this isnt including the insert,nock,fletching and tip,this should put you around 400 grains with a 28.5 inch arrow.
If your looking for all out speed then you want a lighter arrow,keeping in the boundaries of 5 grains per inch.
Im shooting the CX300 with 68 lbs draw and 27 inch arrow and they work great for me.