Plenty of Ozzie buffalo have been laid low with the various .350s, by long-time buff hunters who know what they're doing. For accurate shooting at undisturbed animals, fine, but if the sh!t hits the fan the cartridge is no 'stopper'.

I had a .350 in my hands last Thursday evening, a lovely little Rigby double on a Webley action, owned by Peter P_. we were reminiscing over the rifle, he and Vic P_ killed literally hundreds of buffalo with that rifle in the days of the big herds.

Please remember that experience counts for a great deal in using medium-bores on dangerous game. In Australia 20 years ago, the average Territory hunter would shoot more buffalo in a week than the average North American hunter would see in a lifetime. If you haven't had the opportunity to 'work up' to the medium-bores, by hunting large numbers with big-bores first, you really should think twice. For safety's sake, the 'once-in-a-lifetime' (or maybe twice!) cape-buffalo hunter of today should probably be carrying both a hunting rifle and a stopper in one.
The .350 doesn't qualify.