In Handloader's Digest: Tenth Edition is an article by Ed Matunas, "Loading for maximum PIR" (Power Index Rating) - this being a formula whose calculation is claimed to be an accurate method to identify defensive capability of handgun ammunition. My rule of thumb for my own evaluation is: There's no substitute for cubic inches. I have zero experience with actual need to test my own evaluation, nor have I previously paid any attention to any calculation similar to what PIR claims to do.

Those who have tested such formulae in the real world - I expect there to be very few in this forum - are such things accurate representations of bullet-ammunition "stopping power?"

I'm afraid I won't help you much, but attempting to quantify the unquantifiable has been the life's work of scientists and engineers for centuries.
While, as an engineer, I respect the objective value of the PIR, I believe the real world presents too many variables to provide anything more than a "starting point" for decision-making.
The idea that you should make the largest hole you can works for me.

Regardless of its efficacy,I'd love to read the article just for its insight.

There have been a few studies/reports (google is your friend) but getting a statistically valid sample is a tricky thing when it comes to shooting people. Sometimes the mouse guns work but generally bigger is better. But you knew that already.

try the Sanow & Edwards finding on Cops VS Perps shootings...