Opinions on rifles for DG are like A-holes, everybody has got one. Me included. But, you asked for comments from hunters who have been there. So, here is my 2-cents. Prior to my DG hunt for Cape Buffalo, I wanted a 416 Rigby but could not find one that I could afford at the time and ended up with a 375HH. Then a 2nd one. I liked the cartridge and used it with good effect on a Blue WB last year. I studied the ballistics and liked the longer range of the 375 for PG as well. I believed that the advent of moder bullets like the TSX and A-Frame made the 375 punch well above its weight class. My PH said it was all I needed for Cape Buffalo. I bagged a nice Kudu with my 375 this year with two shots and the first was poorly placed yet it drilled thru and thru with both. Buffalo are bigger and tougher.
A few weeks ago, I was on Safari (my 2nd) and we waded into a thorn thicket so dense that you could not see a buff that was more than 20y away and I am here to tell you that at that moment, I was really wishing that I had brought a 458WM or better still the 458 Lott. As it turned out the buffalos exited the thorn thicket rather than grant us an audience that day and the next day, I took my Buffalo with the 375HH on more open ground. I used 300g TSX ammo and it took four shots without misses to put it down on the ground. None of those shots exited the animal. And to be honest, I was not all that impressed. Would I do it again? Probably. But, If I was going to hunt Ele, I would bring a bigger hammer. I am not recoil sensitive and enjoy shotting 500g full power loads in the 458WM. It kicks more than the 375 but it is not enough more to matter. Not sure I would want to shoot it much from a bench. For any DG besides Elephant, the 375 is probably enough gun. I would talk to your PH about the terrain and cover where you plan to hunt. If it is going to be in tight, dense cover a bigger option than the 375 would be my choice. Yes, your PH will have a stopper and part of his job is to cover your ass, but why intentionally go down that rabbit hole? 416R is a great cartridge. That is the only 40 I would consider only because of ammo availability. 458WM is a good performer for DG. There are others. But those two would be my most likely choices.
Yes, I bagged my buff with the 375HH and no, my PH did not have to shoot a single shot. I could have killed it with one or two shots but was of the mind that as long as it was standing I would keep shooting. My rifle holds 5 shots and I fired four in the span of about 8-10sec and the bull dropped dead at that point. He only ran about 30y and only faced us once. I was never in any danger except the day we stalked into that 10acre thorn thicket. For those few hours, I was walking in the valley of the shadow of death and I was NOT feeling good about my choice. Sometimes you get to do dangerous stupid stuff and survive, lol. The thing to do is learn from those experiences and like you are doing now, try to learn from the dumb things experienced by others.
Use your 375HH on the buffalo and see what your think. Use 300g or 350g full power loads and get closer than 100y. Shoot well and place the critical 1st shot well and then keep shooting. Learn from that experience and then go buy the biggest gun you can shoot well for the elephant. My 2-cents. Enjoy the hunts. Africa is a magical place.