"there's a video or two out there of a guy in body armor voluntarily being shot by a high powered rifle at a distance of a few feet. He stands on one foot as he's shot and doesn't even lose his balance."
Why would he? The guy shooting the rifle didn't fall down... same energy is directed on both directions, fore and aft, every time a rifle is fired. If it doesn't knock down the shooter, it ain't gonna knock down the recipient.
"I'll agree with the .500 S&W. Whether it can penetrate or not, the force of a 440 grain slug at 1600 fps will probably incapacitate someone, most likely killing them"
Uhh... <sigh>... No. See above. Physics must not be a strong subject among the local gentry. If that were true, then all .500's would be single shot pistols, with them either incapacitating or killing the folks shooting them...
.221 Fireball would be the thing in a handgun. You need an icepick of a round.