So I think we all know that it's not smart to call a beautiful girl, beautiful, as she already knows that and most likely hears that on a daily basis. Thus that compliment no longer holds any value, and you come across as an unoriginal.
But at what point does the prettiness of the girl surpass the threshold, in your opinion, of being "too" pretty to be called beautiful, to the point that the compliment still holds value?
Based on math, the uglier the girl, the more value that word holds, but as the prettiness goes up, you get diminishing returns per investment.
The math would dictate that 10 would be too pretty to use that word, but I think the actual threshold is subjective and would differ per person, because one might feel like "it's not worth it anymore after a certain point, because even though you get "some" return on investment, it's not a significant amount".
You've got it all wrong. The target's level of attractiveness doesn't really have that much to do with the strategy.
Either way if she's smoking or kinda dumpy, they will want a compliment if they care about you, and of course it has to feel earned.
And so then the strategic question is: How is her self perception going to affect how she's gonna receive the compliment?
For that reason, hot babes love to hear that they're pretty, because it's a sign that "everything is going normal". And dumpy girls love to hear it because it means that you really think she's something special.
You tell them both the same thing, just at different points in your relationship.