IMO, there are too many variables that would decide this for you. I already said my opinion in the El Paso thread that under the circumstances where the shooter is using an assault weapon, your window of opportunity is very small. If you couldn't flee, then that kinda takes away your choices and you have to stand and fight.
I've been giving this a lot of thought since the shootings, and I'm done carrying too little gun. Texas being an open carry state, I'm going to be carrying at the very least my Shield 9mm with two backup mags. If I print, or somebody can tell I'm carrying, well I'm not too concerned anymore because I need to feel like I would have a chance if some idiot and his AK came into the store I happened to be frequenting.
I'll probably start carrying my 1911's more, as well. And my full sized Sig P226. I've got backup mags galore for all of these guns, and while I would still be messing my pants about having to go up against an assault rifle, I'd have a much better chance than if I was carrying my Ruger LCP with a spare mag. That much I know.