RE: slugs and penetration,
According to a forensics book I have, your typical Foster slugs rarely penetrate the human torso; they end up pancaking or breaking up into a few large pieces. The author did numerous autopsies of people hit with such. Buckshot was the same, rarely penetrating the torso unless the range was very close. This bodes with my testing on slugs on penetrating water bottles; they flatten/pancake upon penetration of a soft target and this inhibits their penetration greatly, but it also creates a much large wound track, of course. People who hunt deer with lead slugs will probably find a similar thing, i.e., the slug resting on the off side that was hit just under the skin.
If you hit what you're aiming at, there's no need to worry about "overpenetration" with buckshot or slugs. So practice, then practice some more.
As for me, I like the standard high velocity 9 pellet load of 00 buckshot (Winchester 00SG). I've tested it at various ranges, and I know where it hits and how it patterns. I like it over slugs for the simple reason of putting nine holes in the target rather than one, which equates to a greater chance of striking a main artery for example, which will lead to quicker incapacitation (which is death).
