I like the 2D+P formula and have used it for years. Seems to give a very fair indication of propeller loads. Easy, "do-it-in-your-head" math as well. Who wants to play with exponents at the field when it's 95 degrees?

Read that formula in a book "everything you wanted to know about r/c" back in the 70's. Works fine.

Has nothing to do with flight performance of a given prop though....

'Race