An IBO rating is a useless factor to consider for bowhunting purposes. In fact, I believe the IBO rating is useless, period. Only an idiot or a misinformed person would try to use the setup that the manufacturers use to obtain the IBO.
Most bows made today will have all the energy necessary for the purpose of bowhunting. Final fps is dependent upon total setup and is strictly an individual result. Set your bow up for accuracy, reliability, and durability, and go hunting.
I have downed deer with my 156 fps and 172 fps recurves. For me, any fps above those speeds is icing.
Who was it that said: "I will take a slow hit over a fast miss, any day."