Shoot the heaviest arrow that provides a trajectory that you are still comfortable with. 13gpp is not bad. Here's a few tidbits to convince you.
A heavier arrow stores more of the bow's energy and carries it to the game. Some evidence of that is in its noise and handshock reduction, and the greater depth at which it penetrates a target.
Through extensive penetration tests, Dr. Ashby concluded that you should shoot a minimum arrow weight of 650 grains for big game (out of any bow), and that you should, also, shoot as much additional weight to 650gr that you can manage and still be comfortable with the trajectory. (He is saying the more, the better).
THE ABOVE IMPLIES THAT SOME LIGHTER BOWS SHOULD HAVE A GOOD DEAL MORE THAN 10 GPP to meet this requirement: in fact, Ashby was able to design an arrow that (through astonishingly many trials) punched through a cape buffalo rib with a 40 lb bear recurve (this arrow was certainly more than 10 gpi).
There is no reason to be concerned about loss of speed with heavy arrows: since the speed of sound is nearly 4x as fast as the fastest bow, one need not be concerned at all about loss of arrow speed associated with heavier arrows, since animals can easily jump the string on the fastest bows (you should just always select your shots on fully relaxed, unaware animals and forget about arrow speed).
For myself, as a split vision archer, I have noticed that I shoot better with a heavier arrow because:
A) it reduces my point on distance to about 35 yards, and makes shots at the back of my hunting range remarkably easy.
B) even though my accuracy may be better on larger game with a flatter arrow, it is worse on small game: I will certainly be able to hit a football at 10, 15, and 20 yards by shooting basically the same way each time, but I cannot discern the mere inches to raise or lower for a squirrel's head occuring at these distances because I am just not able to adjust for inches with an arrow tip in my peripheral vision. So there is psychological advantage.