Carry the gun that you're gonna wish you had.
That's a very nice platitude, but one that simply does not work. You compromise on what you carry. As mentioned, I might wish I had an AR, or a shotgun, or a 6" .44 Magnum, depending on the fight. Wishes are nice, but they sometimes run head-on into the wall of reality. You choose to carry a Glock 19. I might argue that is a compromise over the Glock 17, or the Glock 21. I'll assume there is some reason you have made the choice to go with fewer rounds or smaller caliber. Fortunately our choices (compromises) rarely matter in DGU situations.