He is a client. His job is to put as accurate and lethal first shot as possible into a DG animal. If he does that, the stopping capabilities of a particular rifle are largely irrelevant.
I assume we are really talking about buffalo - a 9.3 would be excellent for a cat and few people will take one elephant hunting. My 9.3’s (63 and 74R’s) are nearly perfect bear rifles. The difference between a 286 and 300 gr A-frame are pretty small. Still, there is a difference.
Obviously, a 40 something in exactly the right place is equally lethal. It is, however, my belief that most first or only one time buffalo hunters are better served with the .375 simply because the transition is so easy from a familiar “deer” rifle. It is also so incredibly versatile for everything else the client will be doing on that hunt. I can use my Blaser .375 with great precision, which for most relatively short modern day buffalo hunts is, again in my experience, what is most important.
Probably the most universally useful Blaser combination for Africa is the magnum bolt head and .300 / .375 barrel combination. Your friend will not find many advocating the .308 / 9.3. The latter is, however, nearly perfect for Europe.
