Just another $.02
I'm not going to get into what you should carry,or even how much you should practice. What I will say is that under stress, you WILL do what you train to do, right or wrong.
SO, you should only carry what you practice with. Rely on "muscle memory" is fine, so long as the gun is the one you "memorised". Having a back up of the same model, or at least identical controls is (to me) an important thing. AndI don't mean a carried back up gun (although that is important also), but a back up/replacement for you carry piece.
Because, Murphy being the clever fellow he is, will choose that rare instance when you regular is in the shop, or the one day that you carry something different (for whatever reason) to spring his nastiest tricks on you.
IF you are going to operate by instinct (and it is the fastest, and so the most desirable for an unexpected defensive situation) then your instincts have to be right for what you will have in your hands on THAT day!
This was brought home to me many years ago, in a harmless way, but it taught me a valuable lesson. A friend dropped by, saying he had spotted a deer up the canyon. All he had with him was his Browning Sweet 16 (and no deer loads). So I loaned him a rifle to take with him when he went to look. He talked me into going along, and taking his shotgun, (so maybe I could bag a pheasant - I wasn't interested in the deer).
No deer was found, but on the way back, sure enough, a pheasant flushed. I had a round chambered, shouldered the gun, punched off the safety, and ...nothing. Punched off the safety again, and nothing. A third try as the bird sailed out of sight, still nothing.
I had decades of hunting with my Winchester Model 12. If I had that gun in my hands, I would have had that pheasant. But the Browning has its safety at the back of the triggerguard, while the Model 12 is at the FRONT. I instinctively did everything exactly right for my gun, but wrong for his.
LESSON: IF you aren't, or can't take the time to think about what you need to do, you MUST have the gun you don't need to think about in your hands. Nothing else will do!
And, if you or someone else's life could be on the line, it is even MORE important!
All else being equal (and it almost never is) bigger bullets tend to work better.