Unfortunately people think that they should be able to achieve bang flops. It simply is not reality. Sometimes it happens, (and it is cool) but it is not the norm.
I know that the original post is asking only about caliber, but key to this discussion is bullet choice. No matter what caliber you choose, it must be coupled with a quality dedicated hunting bullet. If you run without a good bullet you might as well be ****ing into the wind.
I stand in the crowd of a high weight retention bullet that will carry through the target. It must be a bullet that will have consistent frontal deformation. More important than double caliber mushroom is the shape of the deformation. A square frontal area, or flat leading edge will cause the most (largest) permanent wound channel.
Once you have chosen your bullet, then you must limit your effective range to the minimum velocity that the bullet is functional.
Now, with that said, I do not believe that there is such a thing as being over gunned. Bigger is better if you can handle it. My son has shot an elk in each of his first three years of hunting. He is 14 this year, and still carrying the same rifle that he started with at 12. And it is not a .50 BMG. He shoots a 6.5-06 with a high quality, dedicated hunting bullet. All of his elk were taken beyond 300yrds out to 375yrds. All of these elk went less than 20yrds. His first elk at 375yrds was hit in the large shoulder bone on the on side, took out the front of the lungs, went through the big shoulder bone on the off side, and recovered in the meat of the off side shoulder. 82% weight retention, perfect mushroom.
I will just say that you need to put as much or more effort into choosing your bullet as you do into choosing your caliber.
Hope I helped more than adding confusion.
Steve