Momentum is king.
 It's so much more important than KE that we wanted to post this momentum vs kinetic energy calculator here so you can figure out the truth behind the penetration power your set-up is generating. Compare numbers and you'll see that fast light arrows don't come close to the momentum of slower heavier arrows. Check it out below...

Enter a variety of numbers to see how it affects the actual momentum you're looking for.

 

Kinetic Energy / Momentum Calculator

Enter Arrow Weight AND Arrow Velocity then press the "Calculate" button:

Arrow Weight (grains)

Arrow Velocity
(ft./sec.)

Kinetic Energy
(ft.lbs.)

Momentum
(slug ft./sec)