http://bbtools.x10.mx/potencjal/(formulas by Josef Ka)
And for example potential MVP = 9, so it means player is capped if his potential score is between 9,00 and 9,99.
Superstar - 8,00 - 8,99
HOF - 10,00 - 10,99
ATG - 11,00
Perennial allstar - 7,00 - 7,99
etc
Interesting information is that one full level of potential means that player can have all skills better by one full level. So ATG can have all 10 skills = ~15, HOF can have all skills between 14 and 15, MVP can have all skills between 13-14, Superstar can have all skills between 12-13, etc.