Use two blade/smaller 4 blade heads(magnus stinger comes to mind) that are razor sharp, on 10gpp arrows, and you are good to go. Elk are easy to kill if you hit em right. But elk will go forever if you hit them poorly, no matter what weight bow you use. I shoot a 68lb bow at my 32" draw (with 740 grain arrows), and hit a cow in the elbow joint last fall. Penetration was nonexistent, and the cow ran off like nothing had happened. Chances are slim to none on getting through any heavy bone you encounter on an elk.