I have read opposing research about velocity causing death. From my experience, I don't think it does. All of us have knowledge of big game animals that were poorly hit with bullets from mega-magnum cartridges and traveling a long way after. In contrast, no animal is going very far sans heart and/or lungs. What destroys these organs is immaterial. That they're destroyed is.
Were I accorded a hunting do-over, I'd buy a .280 Remington and never need another rifle. However, I know other hunters might see it differently. I'm good with that. What other hunters use to kill big game is their business, not mine. As long as their cartridges are capable of causing humane kills, I'm good. And I will admit, campfire cartridge banter is fun. If a hunting buddy believes an '06 is better at killing big game than a .308 Win, I'm good.