It seems to me that the thing to remember here is how a bullet actually does its killing. Unless the central nervous system is damaged or destroyed, blood loss is all you're working with. In that light, it seems to me that the more big holes you can make for the goblin to bleed from, the better.
The goal in self defense scenarios is to stop the attack as quickly as possible. A .22LR might kill the attacker, but the chances are very good that it won't do so fast enough to prevent him killing you before he expires himself.
A good parallel is deer hunting. A deer reacts differently to being shot than a normal human, due to the massive adrenaline dump than a prey animal is capable of, evolved to be able to help even a badly wounded animal escape from a predator. However, that response is not entirely unlike the response of a human whose body is supercharged on drugs. I've seen deer with phenomenal hits, such as both shoulders, heart and lungs destroyed, by a 45-70 bullet, weighing more than twice as much as the average .45 ACP, and travelling twice as fast, STILL run several hundred yards. The deer was already dead, just hadn't realized it, yet. How bad would it go for you, if a human attacker who was in similar straits got to you, before he later realized than he'd been fatally wounded?
Basically, what I'm driving at here, is that when it comes to self defense, my first choice is a minigun. However, since they weigh about 130 lbs, plus ammo and power source, I've had to look for something slightly more portable. I think that might be a better system than starting with an NAA .22 Short, and then working up until someone on the internet says, "Yeah, that might do it."
~~~Mat