To me this is like arguing about what type to plastic to build your car engine out of. Handguns are not effective for self defense. Even 10mm isn't going to stop someone. Why? 21 foot rule - If someone is within roughly 21 feet they can usually get to you and stab you in the face before you could draw and fire. Then it becomes hard to stop them with a missing face. Hit percentage - Use whatever hit percentage you want, it's not good enough. Most I've seen are below 20% for "trained" officers and that's with most shots inside 10 feet or so. What success rate is within the acceptable limit for you? Sure the chances of having to pull a gun are low, but once we're there, what are your odds of getting a shot off, having it hit a high center mass, and the guy dropping? Caliber just doesn't matter because speed and accuracy are such a limiting factor. If you can make one more accurate shot with a .22, you're better off with the .22.