IMHO, it depends largely on what you are shooting the arrows into. If you are shooting into hard foam, then the lighter, faster arrow may penetrate just as well or even better. Does that traslate into better penetration when shooting at game? I would doubt it, but have no evidence to prove it. I know it is often irrelevant to compare archery equipment to guns, but here is a story with (to me) a surprising result. My buddy was shooting his 7mm Remington mag, and another "friend" who was a know it all type suggested he shoot it into a 1/2" steel plate. He said the 154 gr. bullets my friend was shooting could not "blow through" the steel plate, but his 75 grain bullets could. Sure enough, that was how it worked out. The sheer velocity of the lighter bullets blew through the steel plate when the heavier, slower bullets did not. However, Mr. 75 gr. bullet said that meant they would penetrate better on game. That is not the case, and I do have enough experience with various bullet weights and velocities to know that if I am hunting for Elk or Moose, I certainly would not choose the 75 gr. bullet.