I am curious why you consider a 9mm to be a "shoot to kill" weapon when other loads you've had were not. 9mm is a great little round, but definitely not the man-stopper some rounds can be. (Also don't get me wrong, I love my 9mm, for me the purchase was made because the gun would be fun to shoot more than because I wanted to be able to crack the engine block of a Mack Truck.)

Shooting to wound, is a great idea in theory... in fact the one anti, that I have discussions with on a regular basis, wants to believe that a 20 gauge fired at the legs is enough to stop a dedicated attacker, and while it MAY be is it worth taking that chance? (Its like buying sub-par insurance, it might help you, but if you can't be 100% sure of it what's the point?) I, like you, don't want to kill anyone (ever, for any reason) even hurting someone is a terrifying prospect for me, and if it was JUST me in danger, I'd be less inclined to act in my own defense. That all said, I have a wife, and almost more importantly 2 little ones. The discussion at that point is open and shut, you endanger my kids or wife and we're past the point of a discussion, or even a warning shot. (To be honest this rule applies whether I have my 9mm, a baseball bat, or just my bare hands if need be.)

As for firing a warning shot through the door, I am glad you have the law on lock. That's number 1, know the laws as they stand, make an informed decision. After that, though, I would hold my fire until they were through the door. First off, someone breaking in, I am going to need to replace the door whether they crowbar it or I shoot it, so that point is null. Second, I'd MUCH prefer the police to do the job that I pay my taxes for, if they can arrive before the door breaks, good (in a situation like this every second I can stall before needing to take a shot the better.) (In fact, this is one of the major reason's I think Joey Biden's "Shoot your 12 gauge through the door!" line is moronic.) Third, (and has been mentioned) the longer you have to prepare/identify the person breaking in/talk to the police/get your family out of the area where gun play might be happening the better.