Chances are, if you shoot them in the gut, you'll get your chance to meet them. Very up close and personal.

Where did you get the information that a shot to the gut (i.e., mid to lower abdominal area) is going to do much of anything in the short term? A direct hit to the spine/aorta/vena cava might do it, but that's a pretty small target. A fractured pelvis could give them a bit of a slowing limp, but such gut shots aren't something anyone with training would go for intentionally. Irregardless of caliber.

It's not pain that stops an attacker. And a larger caliber is not really going to be any more painful than a smaller one anyway. I would fear a .32 to the chest a lot more than a .45 to the gut.