Paper ballistics are good for comparisons but don't tell the whole story. Stopping power is partially due to bullet diameter. The bigger the wound channel the better. Elephants have been killed with bigger and lessor calibers yes. You said stopping power so it will go to the bigger diameter bullet.
A 22 250 has similar energy to a 45 70 due to its velocity. The 45 70 will out penetrate a 22 250 by feet due to its big heavy slow moving bullet.
Nothing wrong with a 308 or a 45 70, 2 great rounds.
A 45 70 is not equal to you muzzle loader if and only if you have a modern 45-70 that allows you to use higher pressure loads. Again paper ballistics not telling the full story.
Bullet diameter, bullet construction,weight and velocity all are major players in stopping power.
To me over .375 caliber is a stopping rifle, under that you have some great rifles but less stopping power. Not to be confused with killing power.
9mm vs 45 well there is always much debate, I have never had any 45 fans agree to let me shoot them with my 9mm then they can shoot me with thier 45. Yep I own both and love both.