Years ago, while serving as a reserve police officer, some of the training referred to the "Hatcher Scale Of Relative Stopping Power". Back then the .38 was just being phased out and the .357 coming in as a duty weapon. However, the .357 just made the lower end of the scale as a reliable stopping weapon. The .45 (not a duty weapon at the time) was rated very highly. This is the primary reason I usually carry a .45 now and sometimes a 9mm. For more info check out the following.
http://www.gunblast.com/RKCampbell-Cooper.htm