The 45 ACP is definitely a lower pressure round, at 23,000 CUP for +P loads. The 40 S&W has a maximum set at 35,000 CUP, but the 9mm is the highest pressure loading, with a maximum of 38,5000 CUP.
The 45 is also the slowest, at about 850fps for the standard "ball" load. The 9mm will push a 124gr bullet at around 1200fps. The 40 shoots a 180gr bullet at about the same as the 124gr 9mm.
It's important to know that NO handgun cartridge is a "magic" kind of thing. So many factors play a role in the use of a firearm against a human... There are documented cases, one in particular of a man that was shot 6 or 7 times in the back with a 45 ACP, and drove himself to the hospital and recovered with minimal issues.
A recent case actually caught on video was a law enforcement officer who was doing a traffic stop who was shot by the perp with a .22 pistol. The LEO shot the perp several times with his service pistol (I THINK it was a 9mm...). The LEO then called for backup, and then staggered and sat down... and died. The perp survived, after hitting the LEO with one tiny .22 bullet, in the heart.
All I know is, that I hope I NEVER have to find out what it's like to be involved in a shooting.