It is illegal, however its Africa, and nobody checks and nobody seems to care as lots of ladies and youngsters shoot buffalo with the 30-06, 308, and 7x57 and of course they have a PH to back them up..
Most PHs shot their first buff with a 30-06 or .308 as a matter of fact..The 35 Whelan should do fine. I have used the .338 and 9.3x62 on Buffalo more than a few times, but I do suggest you back up that first soft point with solids for the second going away shot or in case of a charge. Buff shot with the smaller big bores do travel further in 99.5% of the cases..usually until they bleed to death. The 9.3x62 with a handload is legal in most of Africa. It's probably a little better..
I think if I were you I would just get me a .375 H&H or 375 Ruger and be done with it. You'll like it better than either of the other two even on deer size game, but that is up to you.
The problem with this kind of advise is you do not have a stopping round in the lighter calibers, and if you get charged then your selection may be very bad indeed. that is rare but never think it can't happen, I always assume it will. I used lighter calibers early on to satisfy myself I suppose as I am an experimenter and bullet digger. The worked but a few close calls changed my mind and Today I use either a .375 or 416 and ocassionally a souped up 9.3x62 that competes with my .375...
