A well sharpened tree shark will blow through anything. I read online about a guy that hunts elk with them exclusively out of a 50lb bow and has gotten pass throughs on every one. Me, personally, Ive killed deer, bear, and pigs with them and have always gotten great penetration with a 50lb bow and 600 grain arrow. The one that sticks out is the bear I killed a few years ago. About a 200lb sow. I shot her while she was coming down a tree. The arrow entered just in front of her back leg, passed lengthwise through her body, existed her sternum bone and stuck in the tree she was climbing down.
Before that, I had one pass through both scapulas of a young buck and bury in the dirt. Unbelievable heads! I think they can compensate for a poor shot in a lot of cases and my initial thinking was that you are much more likely to hit a critter in the liver or guts than bone thats heavy enough to stop the head, but I havent found a bone yet that they wont penetrate.