Just my two cents. I have had complete passthroughs as well with an old bow, shooting heavy aluminum arrows. I know shoot a new bow with significantly lighters arrows and still get complete passthroughs. There was a thread here recently discussing how the newer bows are getting more efficient at transfering energy to the arrow instead of wasting it through the bow with a light arrow setup. This leads me to believe that you should be getting roughly the same KE out of a new bow-light arrow setup.

I do however agree that a little heavier arrow is a better bet for hunting. I try to fall in the middle weight, somewhere in the neighborhood of 380-400 grains. I get good speed, and great penetration. My last seven deer have been all passthroughs with this setup including a quartering shot that broke the front leg on exit.

Just my thoughts.