I realize there is no acceptable "correct" answer for all of us to this question. All responses are interesting and informative. For me, since I have no need to own and use the biggest and the baddest, the .450 is not a consideration, nor are the hyper 45-70 loadings.
I agree that most of the "standard" loadings will get the job done if the energy generated by them is applied in the right spot, and it will be lots easier on the launching pad and the launcher in the process. Dead is dead, and I have no need to blast anything (on either end!) to smithereens. No quarrel with those of you who enjoy the stout stuff!!
That said, IF the proper style and construction of a "pistol" bullet will get the job done, then what is wrong with it? For any purpose, there are many choices, including among rifle bullets, so we still have the obligation to pick one that will make our quarry lie down quickly with the least amount of potential difficulty. Once again, if an adequately constructed projectile is launched at an adequate velocity and is directed to strike within the heart of the "kill zone", given adequate penetration, the end result is gonna be acceptable, NO?
I kinda like the .444. Nuthin against the 45-70 for sure, but (for me) it seems the .444 will get the job done in a perfectly satisfactory manner. Maybe a better question would inquire about the shooter, since all these firearms have the potential to get the job done!!!