The answering of the last question is where it gets interesting.
There looks to be a real difference between what the PH's use and what they suggest clients bring (other than the 470).
Maybe elephant specific would be different, but for either 458 to be suggested above the 500's (Jeff & NE)etc. is very telling. I think a PH takes into account not only client shooting comfort/ability, but also availability of replacement ammo in case of a mishap etc. That kind of practicality is in their nature I think. That is probably also what leans them toward the 458's for themselves in many cases.
Also, there is a big difference between choosing a gun to take along when hunting with an experienced PH with a stopping rifle and being the PH with the stopping rifle. No matter what the client is using, there are always immediate followups from the PH if needed - not so if you are the PH or on your own such as Taylor was most of the time.