It does get confusing. If your concerned with self defense then you want a bullet/caliber that will penetrate far enough and expand as much as possible. Don't get caught up in velocity and energy to much, your better off checking out articles about proven bullets and calibers. A good example of this is the 357 magnum. The 125 grain bullet is a great man stopper, but poor for deer sized game, (100lb - 200lb game.) Why??? There are a number of factors. The 158 and up bullets are slower but have more ft. lbs and penetrate better on game animals. A 32 H&R mag is faster then a 45 acp but the 45 acp at 800 fps is one of the best calibers out there for self defense.
Check out the Winchester web site for comparison;
http://www.winchester.com/SiteCollec...law_bullit.swf
The 357 sig is faster then the 147 grain 9mm but the results are close if not in favor of the 9mm on gelatin test. The 380acp has great expansion but the penetration isn't up to the FBI standards, (12 inches or more.)
Different calibers do things differently. A 308 Winchester 180 grain bullet at 2800fps can be used for Moose hunting, but so can a 45/70 405 grain at 1800fps.