On the question of solid or soft for the PH- that might depend on which rifle he is using. I have used 500 gr Rhino softs (basically the same as Trophy Bonded Bearclaws) in my .450 Rigby Rimless to back up a few buffalo, and had tremendous penetration.
I remember one shot went in the same distance as a .505 Gibbs solid ( 525gr Woodleigh). (Both shots were fired in between buffalo's shoulder blades- already lying down on the side- and both were found in the brisket.) This bullet, driven at 2400ft/sec., will propably drop or turn a charging elephant cow, (which is more likely to be encountered in an unprovoked charge than a bull), if directed to the brain, because of its penetration. The same can be said about Barnes X bullets.
However- if in country were elephant are likely- I believe PH sould carry only solids, as his job is only to help stop charges, and shoot at the rear end of wounded animals. In both cases more penetration than available from a soft is often requiered.
On the topic of cats- Yes cats die more readily from softs, but so does anything else if adiquate penetration is acieved- (penetration through vitals). They die from solids as well, and can be stopped with a big bore solid, say .458 and up, especially if it is a blunt nose solid or, duel diameter solid.