20# will do the trick if you hit them right. But, score a direct hit on a rib, or worse, and the animal will bound away, perhaps not to be recovered. No doubt, 35 to 50# bows have taken loads of game. But again, get a poor hit and the penetration won't be there. I'm a firm believer in using as heavy a weight bow as you can before your shooting begins to deteriorate. (Not talking repetive target shooting here, in which you may want a lower weight yet, but first shot or short duration shooting.) I'm comfortable with 60# year round, up to 70# when well practiced and in fair weather. Most of my hunting bows hover around 60#. Animals move and jump the string, twigs deflect arrows, and I sometimes make poor shots, so I want as much ooompf as I can manage well to ensure the deepest penetration possible for those occassions when the shot goes bad and my arrow lands in heavy bone or dense muscle, or needs a lengthier pathway to reach the "off" switch. I'd shoot 80# or 90# if I could manage it well. It's up to the archer to find the balance.