Ok...I'll bite...
If you want to discount the prudent response as "macho," then I would argue you aren't looking for honest answers. I doubt that even the neophytes would argue that carrying only 2.8 rounds (because that is the average) would be prudent. Heck, its not even possible! So let's say three rounds. Any takers? Of course not. And here are some reasons why...
What if the assailant is using illicit drugs that dull the pain response? What if the assailant is wearing some sort of body armor? What if the assailant is using cover or concealment? What if they are just so emotionally invested/committed for whatever reason that they continue to function even after having been dealt serious injury? What if there are multiple assailants? What about combinations of the above factors?
The answer is, and continues to be (with no machismo necessary), that you should carry as many rounds as you are willing to carry and can effectively conceal if that's your style.
Another factor to consider is the number of spare magazines you carry. If you are ever in a prolonged gunfight, you may have an opportunity for a tactical reload. Your gun runs on ammo, so top off the tank. This requires you to exchange the partial mag in your gun with a full mag from your belt. The number of full spare mags you carry will determine how many times you can do this, and will prolong the possibility of running the gun dry and needing to do an emergency reload. Bad place to be: in the middle of a gunfight with an empty gun.
So...as many rounds, contained in as many spare magazines, as you are willing to carry and are able to effectively conceal (if concealment is your style).