There are good arguments for both open and concealed carry.
One of the best for open carry is the deterrent effect. If a BG sees a gun on a competent-looking individual, they will probably think twice about what they're planning.
A good argument for concealed carry is you may get the drop on a BG. SURPRISE! However, that brings into play several counter arguments, such as: in a store robbery, are you being directly threatened? Except in specific circumstances, you usually are NOT allowed to defend someone else's property, and you may find yourself in deep doo-doo if you act as a licensed security, or police, agent would.
A good argument against OC is your gun may be grabbed, or you may be targeted. Personally, I believe this to be highly unlikely, as most criminals want it easy and quick. they don't want to possibility of a gunfight with a determined citizen.
A good argument against CC is the time and effort it takes do bring your weapon into play. The key to eliminating this is to conceal as shallowly as possible and practice, practice, practice.
To address your comments directly:
Check the stats, not many OC'ers have their own gun used against them. In fact, very few even get into a combat situation. As for being in a war zone, look at the nightly news...you are already in a war zone, that's why you carry. Only you can determine the necessity of the level of readiness you need in your area. However, the mess is hitting the blades in more and more unlikely places, so beware.
Your figures of 1.5s/20ft is correct. You can stay away from the zombies, but will they stay away from you? The best gunfight is one that never happens. Situational awareness is everything. If you see a potentially dangerous situation or individual, stage a tactical retreat, if it is safe to do so. Get out of Dodge. Read books on SD (there are several good ones out there)and practice avoidance and maneuvering. You may look silly running around your back yard doing this, but it may save your life. If you must stand and defend, be prepared to go 100%. No hesitation. Do what you gotta do. It's better to be tried by 12 than carried by 6. That's why I have a lawyer on retainer and his card in my pocket.
As a side note, I lived in Monroe, NC for 8 years and OC'ed daily, into many different stores and businesses. Never had a problem, either from the "terrorized" citizens, the LEO's, or the BG's. I frankly enjoy OC, it's simply much easier, and, I believe, more effective.
I don't think I've tried to sway you on either OC or CC, it was not my intent. Personal defense is just that, personal, and you gotta do what seems best to you.
Carry in Peace.