For me, it's not about the cartridge as much as it is the platform. I prefer having 17 rounds of perfectly inadequate SD ammunition in my magazine as opposed to 7 rounds of slightly less inadequate SD ammunition. I don't want to have to change magazines in a fight and, more than that, I wouldn't want my wife to have to change magazines in a fight. It's also because I feel that multiple perpetrator attacks are the norm, not the exception and missing, as much as we like to think that we won't, is probably more common than hitting. One might need to deliver suppressing fire too and, there again, 17 rounds in the stack affords you that option. So I want a high cap double stack magazine and I will not routinely carry something that isn't high cap. In fact, I mostly just won't. I would (and used to) carry my Glock 20 because I think that 10mm is better than 9mm or .45acp but it's too hard to train with it and it's a lot easier to carry my 19x and I would be very comfortable using it in a gun fight. Much has been said here about follow up shots. I know that with that pistol, I can put 124 gr HSTs into the chest as fast as I can pull the trigger. If I need to adjust fire for the cranium, no problem. It is exceptionally controllable due to the full size grip and the shorter muzzle and, at least in my hands, I know I can deliver accurate rapid fire shots faster with the Glock 19x than the Glock 21. But I'm a huge fan of the Glock 21 too.