Hello,
Theoretically p crit RATE is capped at 500, which roughly corresponds to 50% chance). There are some exceptions like summons and evis if im not mistaken which can go past 500. I would say that the limit would be 1000 (100%) but don't know an in game way to reach that number.
I wonder mostly how p crit rate scales after 500. Is 700 p.crit rate 70% chance or the curve reaches a plateau? Take for example m crit rate that is capped to 33% even if u have 500 mcrit rate.
Your question is rather interesting, but needs some testing to get an answer. As no1 cares here, especially for summoners, you might wanna ask in eu boards or test it yourself.
BR,
Q.