Wow. My head hurts now.
I worked with statistics quite a bit in college.
Statistics can help you understand some things, but I don't believe they are suited to this discussion. Especially averages.
I carry 27 rounds total. One extra clip.
I feel comfortable with that.
3 or 4 shots? No, I wouldn't feel comfortable with that.
You NEVER know what's gonna happen. Period.
Be prepared with what you think prepared is.