I could be wrong but the method or test I use is to test how the soap lathers best, when considering bowl, palm and face lathering.
If face lathering doesn't work the soap is thrown. If palm lathering creates a shiny, more volumous lather than bowl lathering, I add either argan oil or glycerin to the soap; when bowl lathering. However, this soap doesn't make my top list.
My top soaps create a shiny, thick, slick lather with all three methods without having major differences between the three or additions. My top top top soaps only require a 30 second load and less than a minute to create a shiny, dense (no air bubbles), slick lather in a bowl. Again this is all IMO and I do have very hard water. But P&B establishes itself firmly amongst all my criteria. I also appreciate the inclusion of ingredients such as coconut milk within the product.
With OSP I find I get an awesome lather when palm lathering, bowl lathering takes me longer (silvertip used with all the soaps) and isn't as shiny as what I create on my palm. As with anything YMMV but ultimately it's what works for you.