RE: Best caliber?
You will benefit from a bigger bore like the 50 or 54 but alot of it depends on the bullet size too!
I would be tickled-pink to go elk hunting with a 45 cal White M98 with one of those 460 grain Powerpunch conicals.
On the other end of the spectrum, I would not desire to hunt elk with a 50 cal roundball or with a 195 grain sabot/bullet in it.
If you' re undecided on which caliber to buy, the 50 offers the largest inventory of bullets & accessories & with the proper powder charge, bullet grain & bullet placement combination, it will kill an elephant.