Two Law Enforcement Officers, Marshall and Sanow, wrote several books, among them "Stopping Power, Street Stoppers, and Handgun Stopping Power." These three are sitting in my book case looking at me as I write this. What is different about their books is their approach to the question. They forgo much of the ballistic jello and velocity testing, although there is some of that, and instead pursue "what really worked".
They did surveys of all the law enforcement agencies that would respond as to their involved shootings, inquiring as to caliber, bullet, load, etc. and limited their results to one-shot stops. One shot stops because that is a good indicator of stopping power, as multiple hits with anything are likely to be effective. The results are fascinating to read, and not at all what you would expect. Stopping power seems to be greatly dependent on (1) where the subject was hit, (2) the bullet design. Sometimes a .25 ACP was lethal, and sometimes a .44 Magnum failed. 9mm with modern JHP loads seemed all around very effective.
Their books are becoming slightly obsolete now, simply because there are new bullet designs and new loads constantly under development, and more data has been produced from their use. However, their last book had such developments included as Gold Dot, Hydrashok, etc., and the books remain a "must read" for those interested in what works and what doesn't.
DG