Also possibly of interest: <https://forum.effectivealtruism.org/posts/nqJDGjccGLDKdGnXE/social-impact-of-the-donations-of-the-10-richest-people-in>, <https://forum.effectivealtruism.org/posts/wahhPpkKnCoGSMZzq/the-billionaires-philanthropy-index>. Particularly the second; you might be able to tweak it to achieve what you propose.
Also possibly of interest: <https://forum.effectivealtruism.org/posts/nqJDGjccGLDKdGnXE/social-impact-of-the-donations-of-the-10-richest-people-in>, <https://forum.effectivealtruism.org/posts/wahhPpkKnCoGSMZzq/the-billionaires-philanthropy-index>. Particularly the second; you might be able to tweak it to achieve what you propose.