I've only killed 2 bulls - one average body size and one very large body size. Shot through both with big Snuffers, one bow at 58 lbs and one at 65 with 620-640 gr arrows. That is into the fletching with arrow out the offside.
You really realize how big they are when they are on the ground...they are a BIG critter compared to a whitetail. I don't feel overbowed in the mid 60's on elk, and I wouldn't feel very good under mid 50's with heavy arrows. Of course I want to shoot big broadheads. They are tough animals, and I REALLY want 2 big holes for tracking an elk in typical elk country.
R