I guess that if you are applying the highest scores to the most useful stats, like 18 to Str for a melee fighter, then elite would be the +1, super-elite a +2 and perfect a +3. But at the same time there is not much difference for a monster having super-elite of perfect as most of the useful stats would be near max with super-elite. perhaps +2 for perfect? But for every second monster with perfect add another +1 to EL.
But why would you want a monster to have perfect stats? Isn't that too unrealistic?