“Stopping power” with regard to firearms is a meaningless term. There are a number of factors that determine how incapacitating a round is–most significantly, how deeply it penetrates and how well it expands–but these measures are complex, depending on the speed of the round, weight of the bullet, configuration of the jacket, what kind of material it has to penetrate through (leather, fur, and wallboard will tend to plug up any hollowpoint round, making it act like a FMJ), and cannot be simplified to a simple calculation of energy. FWIW, it appears that momentum is actually a better measure of “stopping potential”, but again, that’s only a general guideline. While I can’t find a direct link to the study, the FBI did an assessment based upon forensic data which demonstrated that the 125 grain .357 Magnum JHP out of a 4" barrel gave a 92% “one shot stop” rate for center of mass hits. IIRC, the 230 grain .45 ACP JHP gave something like 85%, and it went downhill from there. This is field data, though, and is therefore limited and uncontrolled in terms of environment and reporting. Here (warning: PDF) is a dissertation on ballistic wound similuation, which will tell you more than you ever wanted to know about ballistic trauma simulation.
The 10mm Auto was an attempt to replicate the same penetration and energy of the .357 Magnum in an autoloader. (The .400" round was selected, in part, because it offered greater powder capacity…and no doubt because Col. Jeff Cooper, who was part of the development effort, is a .45 ACP afficinado and wanted nothing to do with popgun rounds like the 9mm.) The .40 S&W was an attempt to package the low end ballistics of that round into a more comfortable size.
Essentially, once you’re past the issue of sufficient penetration (which rounds like the .22LR and .25ACP do not assure) shot placement is the largest factor determining how effective an individual shot will be. One carefully placed 9mmP is worth a magazine’s worth of .40S&W that all miss the target. General rule of thumb is to get the heaviest round you can comfortably and accurately shoot, be it a .38 Spl. or a .45 ACP. (A .44 Mag or .50 AE is probably taking that to an irrational extreme, though, with respect to a human target.)
But here’s to hoping you never have to find out about this firsthand, eh?