Have seen buffalo taken with .416 "softs" including the 400-grain Nosler Partition, Swift A-Frame and Trophy Bonded Bear Claw. All penetrated at LEAST 50" on angling shots, and retained at least 90% of their weight.
If I were going to hunt buffalo again, would probably choose the Swift Break-Away, as it feeds very well, and results more tissue damage than conventional solids. But am also skeptical about the still-advised soft-then-solids advice from many PH's, because today's "softs" penetrate so well, and are more effective.
Might add that the PH I know best, and has the most experience with buffalo, has the same opinion about the soft-solid tradition. He's now retired, and grew up when solids-only was the rule. But then he culled hundreds of buffalo in what was then Rhodesia with the original lathe-turned Nosler Partitions and changed his mind--and they were 180s from a .30-06. They weren't shot at night with head-shots, but during daylight when herds were driven toward him.
