Per my posts above, penetration kills, but it is not everything. A big, heavy bullet with good cross sectional area moving at sufficient velocity will not only penetrate, but transmit a lot of energy to the target and impart shock and stopping power. This is what I think Taylor was trying to get at in the first place.

I am sure a .300 WIN mag with the right bullet will fatally wound/kill a buffalo just fine. You just don't want it to die after it has run over or through you. Something like a .450 NE or bigger keeps that from happening. After a certain point high velocities as a component of ballistics help for flat shooting at longer range, but provide only so much benefit up close.

As has been said by a wiser man than and long before me, a .58 caliber conical from a blackpowder muzzleoader may not penetrate end-to-end and exit the other side of a moose, but it makes an awful big hole going in. A .72 caliber even more so...