Anecdotal, but a close relative was associate director of P&G R&D (Beauty division) for three decades and that figure has come up quite a bit in conversations I've had with him -- he's said all the research they did always just backed up that SPF was the only thing that had serious practical value, that nothing else really matters in comparison (I can't remember ever asking how much skin tone changes this figure though, I should really ask home about it next time I see him).