There' s the answer to your KE question. The reason you' re getting more KE out of the light, fast setup is you changed to a higher performance bow! If you' d put the heavy arrows on the new bow, they would most likely get a bit more KE than the lighter arrows.

As for the lack of penetration, I' m one of the few heretics on the site that firmly believes in heavier arrows for hunting - especially for bigger stuff like elk. I' ve been arguing with these guys over light vs heavy arrows and penetration for the past several years, and the archives are full of those threads.

If you' ve gone two years without a passthru, then I' d say you' ve done a pretty good field test on your light arrow setup and maybe you should start thinking about adding some weight to your arrows.