Guys, assuming you are useing the same bow set at the same weight for the heavy as well as the light arrow they will generate very near the same ammount of KE.

You could actually have a set up where the light arrow would generate more KE than a heavy arrow. There is a point on both sides of the scale where you will get diminished returns.

What the heavy arrow does is generate more momentum than the lighter arrow. Again provided you do not go too far into the heavy side of arrows.