If you do a little research online on broadhead penetration and lethality, the name Ashby is going to pop up. Ignore most everything else and look into his research. He has documented thousands of archery kills on big game in Africa and has literally written the book on what kills best.
Some of the highlights:
1) 3:1 ratio, length to width
2) single blade broadheads penetrate universally better
3) Replacement bladed broadheads fail >50%, mechanicals are even worse when impacting heavy bone.
4) Single bevel on the cutting edges matched to the fletching induced rotation of the arrow increase dramatically the degree of penetration, but will reduce penetration if it does NOT complement the rotation of the arrow
5) There is no corrolation between number of blades on the broadhead with the blood trail (THAT one surprised the heck out of me)
6) steel composition should be hard enough that the blade will snap before it will bend...bent broadhead tips ruin penetration.
7) Heavier broadheads get better penetration, high FOC (forward of center) amplifies penetration on the heavier broadheads. (In other words the further forward the balance point of an arrow, the better it sticks in!)
SHARPER! SHARPER! SHARPER!