Now, to avoid controversy, I am NOT going to assert that the .45 ACP is a better combat round than the 9mm! BUT, there is a reason why U.S. Special Operations forces are today buying specially made custom M1911A1-type .45 ACP handguns to replace the 9mm's they were using. And it is not just to complicate logistics problems....
No, it isn't to complicate logistics...it's because by law they must use BALL ammunition. .45 ACP ball will always be more effective than 9x19 ball. If i lived in a retard state like New Jersey that prohibits HP ammunition for its citizens, I would carry and use nothing but .45 ACP. I don't, and I don't. With a good JHP there is just not that much difference in effectiveness, assuming you chose the proper load.