Not QUITE the same, but in my super hero campaign I explain it like this : up to 20 is what you can expect to see people get to who are dedicated (Muscle boys on the beach, professional / Olympic athletes, etc...). Between 21-30 is characters who are still human, but legendary. If Hercules was a real person that myths were created about he would be near str 30, Bruce Lee (he of the so fast you can't film it) would be 23-25 dex, etc...