Given the incredible advances in bullet design of the last 30 years, caliber is a lot less important than it used to be. Still, the logic remains that a bigger bullet hits harder, digs deeper, and has the potential to do more damage. But only if you can place it well! While I am limited by local ordinance to a 38 revolver, I feel adequately armed, because I carry good ammo. Personally, I'd rather carry my EAA Witness in 40 caliber because I shoot it better, it holds more ammo, and I can reload it faster. Still, the Model Ten S&W I wear is a lot better than nothing, and I practice enough to feel competant with it.
Having said all that, if I knew I was going to be in a Dark Place, I'd be carrying all the ordnance I could, with an AR-15 and a shotgun close at hand!
Papajohn