Also, GPP is just a ball park figure to get you started....bow weight is NOT part of the equation really as far as the 'numbers' go.
Arrow weight and speed is where you get the numbers....the arrow got its speed, but it does not care nor does it know the bow weight. It is what it is.
580 Grains at 187 FPS has numbers you can find out for KE and Momentum.....but whether that arrow was shot from a 50# bow or a 70# bow is not in the equation.
And like stated earlier, 'Momentum is where its at'.