Right now I own 21 1911's and 7 Beretta's, amongst my 75 and guns I own.
If I am going to a fight my secondary weapon, a handgun, will be a 1911. Would I have a problem with a Beretta, nope, but as with the 1911 I want to acquire and bring my own magazines.
As to 45 vs 9mm. I have been in several firefights where I had to go to my 1911. There were a couple where I went to my 38spl too.
AS with the 9mm, in Vietnam the high speed low drag guys like to carry Hipowers of course in 9mm. Caliber is only important if you miss a lot. Most of us that can shoot, caliber isn't important at all. It is good hits that win the day.
In a military fight if you are in a situation that the amount of rounds in your secondary weapon is the make or break, you are already screwed. A different or bigger caliber ain't going to save your ass. Any more than more rounds in the caliber that you have already been missing with will.
Use the pistol or revolver that you have the most experience and confidence with. Go on and anguish over another piece of gear.
If you don't know already, learn how to fight the weapons you have, practice and be ready. Oh, clean and maintain your weapons too. That includes Glocks.
Good luck.
Fred