Also when a manufactuer states a gpi, is that the bare shaft or is that the complete arrow?
That is the bare shaft weight.
The weight of fletching can vary from one brand to another and even within a brand.
The weight of the nock and insert can also vary from one brand to another.
The main thing to be concerned about is the arrow spine shooting a 70lb bow you would be better off looking for an arrow in the 340 spine range but once again that depends on the brand of arrow you are looking at.