the caliber question is an important issue. a clear and definative answer to this question would be of immense value to anyone concerned with their personal safety.
at the heart of the debate, as was pointed out, is the 'light and fast' vs 'slow and heavy' question. from speer #13, maximum velocities in each case:
9mm, 115gr, 1258fps: energy 182kk
45acp, 230gr, 916fps: energy 193kk
the mighty 45acp is the clear winner, by 6%. of course the real self defense load would not be the 230gr ball (used above) but gold dot hollow points, in which case:
45acp 230gr gdhp, 893fps: energy 183kk
so the mighty 45acp is still the clear winner, but by 0.5%. (until the next guy posts with data gathered using a slightly longer 9mm barrel or slightly shorter 45acp barrel.)
HOWEVER discussion (and hopefully FINAL resolution of this important question should be contained within the bottom-feeder (autoloader) forum. this would be a convenience to revolver shooters who seem inexplicably but blissfully oblivious to the entire debate.
38spl, 110gr, 1134fps: energy 141kk
38spl, 158gr, 967fps: energy 148kk
357mag, 110gr, 1693 fps: energy 315kk
357mag, 158gr, 1265 fps: energy 253kk
just mho.