I use a 458 Lott (23'' barrel, 480 woodleigh bullet soft and solid) for 15 years and I had to back up, elephants, hippos, buffaloes (from Benin, CAR and Tanzania), lions and other game and I never been disappointed in the field. Excellent caliber for hunters and PH. Just my experience.
Which make is the rifle ?
My ph in Zambia also took a .458 Lott (Brunner with Federal bullets).
He prefers only soft nose on buffalo,even in thick cover.
And you ?
p.s. a awesome boss you got there