as one old fart to another oldfart, I in my prime carried a revolver for a duty pistol, and was an instructor as well. There are many ways to carry extra ammo, and one of the best is a six-round set of loops on a belt slide. With these on the right side hip, if you are right handed with proper technique, and practice you can load two rounds at a time, and three with much practice. Far faster than a speed strip, and far more easily concealed than speed loaders unless you carry them in a coat pocket.
As far as the number of rounds needed to carry it is a crap shoot. The average rounds fired in a stand up fight by police officers has been for over 40 years about 7 rounds total, and that includes the bad guy shots also. These are FBI record stats of ALL RECORDED police shoot outs.
My first incident in 1977 was on the unusual side, as it lasted for 13 minutes according to radio logs, and not only involved shots fired but, two autos that I and my opponent also used on each other trying to kill each other. By the way, I was a police officer for 20 years. At the end, his car burned, and mine had to be towed. I fire eleven rounds, and all combatants survived.
My second, was more traumatic if that makes sense and occurred at about mid-night on June 19th, 1978. I fired 5 shots with very positive results and it started, and was over in seconds. No one else got a shot off.
My point is, I needed more with the revolver, and less with the auto, and the difference in fire power made no difference. It was the circumstances were different.
If you have fired 6 rounds, and you are still fighting, it is time to change tactics, and leave the area if possible. What you are doing is not working that well.
My last incident was a situation where I had to stand and fight as there was no place to go. Both men in this incident also lived, but left the scene in ambulances. I on the other hand hunted empty brass with the investigators, and wrote pages of reports. The incident went uncontested and both me pled guilty.
The best safe guard is to be ever present of you surroundings, and the people in them. Evaluate constantly whom is in your immediate area. Sounds complicated, but it is a way of life for me, and has been for 40 years. The survivor is the man that knows where the exit is, when the fire starts.