I have heard that smaller diameter arrows are better for penetration, but I'm not sure if it's true.
KE (kenetric energy) is a strong determining factor for the penetration. Arrow weight and speed are factored into the equation. weight*weight*speed / 450240 gives you your total KE.
The fact that both of your bows are on 70lbs has little to do with how much penetration you will get in comparison. For example, a PSE Omen set on 60# at a 29" draw will still shoot faster than my Element even on #70 at the same draw.
You would need to know the total grain of your arrows (inserts, nock, gpi*inches, vanes, field tips) and you would need to get an average FPS on a chronograph and then use the formula above to determine who should be getting more penetration.
Again, I've heard that smaller diameter arrows have been penetration (hence why carbon is better than aluminum).
Hoyt Rampage XT
Tru Glow 4 pin sight
Hoyt Pro Series Stabilizer
Hoyt Ultra-Rest Drop away
Easton Axis Arrows, .400, 382 grains
Rage 100 grain, fixed blade
Alpine 5 arrow quiver
"Now then, get your weapons--your quiver and bow--and go out to the open country to hunt some wild game for me." - Genesis 27:3