Hi rookhawk,
Excellent question.
Any PH will respect you greatly if you ask them that same question.
Also, if you like books, do read the better than excellent: "Africa's Most Dangerous" by Doctor Kevin "Doctari" Robertson".
He devotes an entire chapter to the subject of bullets for buffalo.
That being said, the following is my feeble opinion:
Unfortunately, every rifle usually has its own particular quirks.
So, there is no easy formula to find a soft and a solid that will strike the same spot as each other.
You just have to try them in your specific rifle.
Also, factory live ammunition limits your choices somewhat (but not enough to worry about).
However, many buffaloes are taken very thoroughly with factory loaded .375 ammunition.
Some PHs even prefer to use factory ammunition themselves, because much of it is so well suited to Africa these days (unlike 30 or 40 years ago).
Yours truly has only shot one buffalo and so please do take my recommendation with a grain of pepper.
My opinion on this subject is based primarily on experiences of several PHs and quite a few fellow clients that I have discussed calibers and bullets with over the years.
Regarding a soft for heavy game, I feel that there is no bullet as reliable as the Swift A-Frame, at least none that is easy to find on sporting goods store shelves when you need a box or two.
Even the very best ones that are difficult to find, do not really offer any better performance than the A-Frame, some may equal it (Bear Claw, North Fork, Rhino, etc., etc., etc.) but none surpasses it, as far as I can tell.
Also, the faster you drive your buffalo soft point, the more you need something like the A-Frame.
The .375 H&H is not a super high velocity cartridge (like the unnecessarily fast .378 Weatherby, the Remington Ultramag, and etc) but it is not a low velocity cartridge either.
So, a properly tough bullet is called for when using it for heavy game.
As a side note, do not be lured into using the "sort-of-similar" Nosler Partition in your .375 for buffalo.
It is nowhere near as tough as the A-Frame.
The Nosler might or might not be adequate for buffalo in much larger/slower calibers but, in the .375 bore, it is too quick to expand and fragile for the very thick/stout/impact resistant bones in heavy, dangerous African game - IMO.
Otherwise, the NP in .375 / 300 grain is one of the best bullets for pretty much any other species, including most "normal" animals in Africa or in fact, anywhere in the world.
As for a solid, you are wise to want one that impacts to the same point of aim as your soft.
If your rifle happens to feed and shoot to same point of aim, a solid with a slightly flat tip ("meplat" shape), these tend to track straighter through flesh and bone than round nose ones do.
However, virtually all of the Pre-War Nitro Express Cartridges used round nose softs and solids to take thousands of just about every species in Africa so, flat nose vs round nose is not a huge issue.
Also, as "solids" go, the monolithic types (solid copper or solid bronze or solid brass, or an alloy from some combination of these metals, swaged or lathe-turned to fit a specific caliber) are the very toughest of them all.
However, a thick steel jacket over a bonded lead core (such as the Woodleigh design) will usually pass clean through a buffalo on broadside shots and pass most of the way through a buffalo lengthwise.
Even on lengthwise shots, into an already hit and now fleeing (or charging) buffalo, the lead core "solid" (full metal jacket) has been known to exit the opposite end of buffaloes on occasion.
So, a monolithic is not the deal breaker, if a Woodleigh or similar design is more accurate in your rifle.
I believe Remington and Federal both, currently offer live ammunition in .375 H&H with the 300 grain A-Frame bullet - this would absolutely be my first choice.
Federal might also still be offering the "Trophy Bonded Bear Claw" 300 grainer in .375 H&H live ammunition.
The Bear Claw is an excellent buffalo bullet as well, by all accounts.
However, finding it available for sale is dodgy, at least where I live (and the .375 H&H is no doubt more popular here where I live than it is in the other 49 States, across the USA).
I wish I was going buffalo hunting and you were staying here on my often quite boring job.
Cheers,
Velo Dog.