I give up on the speed/arrow weight/KE/momentum debates. Just shoot what works best for you and be happy.

A buddy of mine was at a pro shop yesterday buying arrows, and while I was in total agreement with the weight/spine of arrows he was sold, I disagreed with the pro shop owner's blanket statement. The owner said he has proven that the lighter faster arrows always penetrate farther into his targets! The owner also said that within 20 yards the penetration was the same but at longer distances the lighter, faster arrow always penetrated more. I didn't want to get into a debate at the time and just kept my mouth shut.