I’ve used longbows in the 55-65 pound range, combined with a cedar arrow tipped with 2 or 4 blade heads (550-625 grains) with good results. I like 2 blade penetration, but I’ve also enjoyed more blood on the ground with 4 blades. I haven’t had any penetration problems with the 4 blade (Magnus with a bleeder).
The last bull I shot gave me a sharply quartering away angle at 20 yards. The cedar/4 blade arrow from the 60# longbow struck just in front of the left hip and exited in front of the right shoulder. Nearly a complete pass through since the broadhead had completely exited the hide. He went 50 yards.
55 pounds is plenty. Good luck and have fun!