My experience (and from the experience of others that have said the same thing to me), with the advent of good tough expanding bullets that can't break up, the use of expanding bullets trumps the use of solids on buffalo, hippo and even elephant.
With a Barnes TSX, or a Swift A-Frame I'd expect at least as good (or probably better) results on buffalo then with any solid you can buy today. Some good mono-solids might be nice to have along in case you need to run a few through from the south end of a north bound buff after the 1d st shot, but overall I'd prefer the expanding bullets I just named.
Unless you strike the spinal column or brain buff seem never to drop at the first shot, so some solids in the mag may be good, but that is not as "written on tablets of stone" as it was in the 70s and previously. The new expanding solids like the Barnes and the double bonded Swift A-Frame the 1st shot is likely to do the job, and you'll find the buff down after it's first run.
