OK, been watching this thread thinking no way was I going to jump in yet here I am.
What I'll say will be in my hunt report if I ever finish the thing. About a year and a half ago I bought a Ruger RSM in 375 H&H for a 2024 buffalo hunt; didn't even want the thing, didn't trust a medium caliber for buffalo but that's just me. Anyway, I bought the thing and immediately sent it to my gunsmith to have it modified the way I like things and took it to TZ. I have to say I was really amazed that it did what it did; one shot, express sights, 104 yards, down and out.
Now, I've never fired a 375 Ruger in my life. I'm sure it's terrific but really it only has about 100fps over the 375 H&H according to what I read; that's in the "so what' range. I handload everything I shoot. What I took was 2534fps using a 300gr mono bullet from a 23" barrel. That is about what a 375 Ruger gets out of a 22" barrel; again, "so what". Velocity isn't everything and in this case it's almost meaningless.
Yes, the rifles in 375 Ruger will likely be a bit lighter, and a bit handier and that's great if you need that. The comments about ammo availability is probably true enough but who the hell is so poor at planning that they don't take more that enough ammo for their hunt? Personally I took 40 rounds of 375 H&H shot 1 at the bull, a few more checking zero, and gave the rest to my PH when I left.
My reasons for going the 375 H&H route were simply esoteric; I wanted a classic style African rifle in a classic caliber and the rifle/caliber combination fit the bill for me.