There are no certainties in hunting. A friend took a cow Elk with a 405 grain Laser Cast bullet over black powder with his Sharps rifle. She fell in her shadow. I've seen Elk hit with Wundermags that required hours of tracking... Upon opening them up I've been amazed by how far they traveled with that amount of damage. Sometimes you hit the off switch. Sometimes you don't.
Anecdotally, with Black Bear, Deer and Elk, it's a GREAT hunting cartridge in my experience. Put it where it goes and there will be meat on the ground nearby even at black powder velocities. I personally have not witnessed better performance pushing it to "Ruger" levels, in fact the opposite might be true. Not enough samples to say absolutely though.
I'd be plenty comfortable using 45-70 to hunt anything so long as the it was a load that shot well in my rifle, including blackpowder.