So many factors go into answering the original question. It is different for everyone. If I had no plans to hunt big dangerous game overseas and could only use one bow, it would be one that is in the upper 50#'s at my drawlength, which is between 29.25 and 29.75" depending on the grip. The long draw gives me some extra energy that someone with a shorter drawlength doesn't get, so let's me get away with a relatively lighter bow and still good performance. This should be enough comfortably to account for stand hunting in cold weather with lots of garments on. It also helps to account for getting some minor injury, sickness, muscle fatique, etc..., not to mention longterm decreases in strenth.
With that being said. the hog I shot last week was shot with a bow that is around 65# at my draw length, and since I shot my turkey with a recurve that is 57# at my draw length, I have only been shooting 2 bows. One is 65# and the other was set at 76# at my drawlength. I just tightened the bolts to bring that one up to 81-82#, and have a bow on the way that should be a little over 86# at my drawlength. That will probably seem a little stiff until I get accustomed to it. The only reason that I am shooting the heavier weights is to make the lighter bows easier, to maintain strength, and to be ready in case I get a chance to chase Buffalo again.
Terry, I am not sure what was meant by no gain, unless they were referring to the animal already being dead. The argument of diminishing returns is a poor one that has never been quantified. If you only got 90 percent (or even 80%) performance gain per pound for a similar bow over 70 pounds compared to bow in the 50# range, that would be substantial.