Impossible to say, due to relativity. A Stacy is simply a girl that AFOG's all her female peers. She is more attractive in her manner of expression, aswell as her body and thus has more social control due to the fact everyone respects her.
This means two things:
1. A girl who is a "Stacy" in one environment could be on the bottom rung in another. You, or I, or anyone, considers a girl a Stacy simply if she is more attractive than the majority of girls we encounter. If someone was native to an environment (Romania), the majority of girls would not be Stacies to them, though they might be to someone else (Dekim).
2. For every one Stacy there is, there must be several non-Stacies (Betties) to provide her "back-drop". So the more Stacies there are, the even more Betties there must be, technically reducing the amouint of Stacies percentage-wise.The 80/20 rule will prevail. All countries have 20% Stacies, and 80% Betties and Belows.