9mm is a marginal stopper under the best of circumstances. Shot placement is important, but it is with all ammo. Thus, given equivalent shot placement, .40 or .45 will do the job more efficiently.

It used to be said that if you bought a 9mm, you were buying the pistol, but if you bought a .45, you were buying the best ammo.

Now, there are many great designs in a more effective caliber. Use your 9mm as a cheap practice understudy and get something more effective.

If you use a 9mm, the best you will do with the best ammo and the best shot placement is about 85% as good as a .45. If that is good enough for you, then get the Winchester 127 grain +P+, which just about turns the 9mm into a stopper on par with a good .40.