The reason the Army adopted the .45 in the first place was that the .38 caliber pistol was too weak when used against the Moro tribesmen in the Phillipines, and hence when the .45 was successful in shooting and stopping doped-up insurgents, it became the M1911 service pistol.
I own a Beretta 9mm, and hope to buy a Kahr 9mm for concealed carry, regardless of these facts. Why? Combat engagement ranges are usually in excess of 50 meters, and personal protection situations usually are less than 10 meters. I'm gaining concealment of a smaller weapon for the trade off in stopping power (particularly at distance). Plus I plan and train to shoot two rounds center mass of target, and then re-evaluate the threat.
So, it really comes down to what you're comfortable carrying, shooting and hitting your target with.