The impulse that is available for penetrating a deer - the force times time - is equal to the momentum of the arrow. Doubling the weight of the arrow will lead to about a 50% increase in momentum, about a 10% increase in energy, and on most hits, about a 50% increase in penetration.

But you' d pay with a big decrease in speed. Say a decrease from 300 fps to 225 fps, if you were starting at 300.