I guess I am asking, since you all know far more than me, does a heavier arrow have better penetration?
In a nutshell... YES. Whenever you've got some time on your hands, you should read this.
www.tradgang.com/ashby/
I will say that a light arrow CAN penetrate as well as a heavier arrow, but ONLY if it is driven with enough speed to equal the momentum of the heavier arrow: A 350 grain arrow @ 300 fps and 70 ft lbs of energy can equal the penetration of a 560 grain arrow @ 186 fps for 43 ft lbs of energy because they both generate near equal momentum.