Here`s the way I look at it. There is a bewildering amount of bullets because competing companies developed different bullets to win over the future gun sales. Each bullet was supposed to "out do" a bullet of a competitor and by doing so they sold rifles, many new bullets were superior to previous ones. Hunting different animals presents different problems to solve, to be successful, some animals you can not get very close to, so you will need to have a bullet that gets to the target from longer distances, to be successful with the hunt. Those bullets have to be faster to accomplish this.
The faster the speed the less time the bullet has to be effected by the elements working against the bullet doing what you want it to do, such as wind and gravity. The "faster bullet" of two bullets the same size and weight will impart a "greater shock" to the animal and thus have "greater kill potential". Increasing speed has some negative effects though, for instance, shoot a squirrel with a 22lr and then one with a 22 mag. if both hit the center of the body they will no doubt be dead but the squirrels body that is hit by the 22 mag will be blown to pieces,if you are hunting for meat in this instance you dont want the body blown into pieces, the correct bullet, in this case was the 22lr and if you intend to shoot squirrels from longer distances then a 17hmr would be better yet, it`s faster thus more accurate at longer distances.
Hunting dangerous animals is best done from a distance and if your target is to be something that is large you will need a fast and damaging bullet, that overcomes the elements and gets the job done. There are places on the Internet that discuss the appropriate size bullets for the animals you intend to hunt. What I have said is overly simplistic and as far as ballistics goes, it`s a very complicated subject that has many opinions to ferret through. I tend to look at it as I do computers, it finds me the answers and I really do not have to know how they work. If I find that the consensus is that a certain bullet works for a particular animal, in a particular part of the country, I`m interested in hunting, thats what I`ll use until I find something else that works better.
One could spend a lifetime on the subject and still not be able to answer all the questions but reading the various hunting books and magazines will get you closer to the appropriate bullet for the animal you are interested in hunting.