Close in hunting, I used 11.5 -13 gpp. Killed after with a near 14 gpp. Slow arrow. However, once I internalized the flight of a 9.5-10.5 gpp, I see the advantages.  Seems my stumping arrow is reaching out to 25 plus yards, easily hitting the spot.  Up close, in the brush of mtns, I could see grain per pound above 10.  They do sink deeper in my test.  But as I rebuild my shot sequence, and draw gets above 28", I see the arrow speed move up.  More speed helps the 450-485 grain arrows hit harder.