"Gut shot" hits may effect a psychological stop, but that is true of any hit. A shot into the abdomen may hit the abdominal aorta, the spine, or the pelvis, any of which may greatly increase the incapacitation effect.
A pelvic shot will NOT keep a bad guy from continuing to fight, so if he has a firearm, don't just stand there and admire your handiwork. We should also keep in mind that not just any old pelvic hit will do. The hip joints are your primary pelvic-area targets. And, the ammo must be powerful enough to break things. I wonder about the .32 pocket pistols, especially, in this regard. Particularly large opponents also present a complication, in that their guts will steal much of a bullet's thunder before it reaches the important structural parts.
The crouching posture, typical of humans in body alarm reaction, will rotate that big belly to a position where it better covers the pelvic area from frontal shots. Not all criminals are skinny crack-heads and meth-heads! The portly gangster look is quite popular these days.