I don't think this is so. A hit to an area of the body that will cause a person to stop with a smaller bullet will have the same effect as a hit from a larger bullet. If you're talking about a .45 nicking a blood vessel that a 9mm may miss, I suppose that's possible, but we don't rely on exsanguation to stop violent attackers. Look at the diamter of a 147 gr expanded 9mm and an expanded 230 gr .45 ACP. Not much difference. Also, any benefit that the larger bullet may carry is outweighed, heavily IMO, but the greater magazine capacity and carryability afforded by the smaller caliber.As you said you are at a root level stabbing someone with a bullet. The bigger the bullet the bigger the stab. You have a higher chance of getting something critical with a bigger bullet.