Overvoltage protection / Transient

Hi, I´m designing a hardware using Me/Wi-Me models and I´m planning to protect the circuit with a polyswitch (BOURNS MF-R050-0-99) and a Zener 1N5335B (3,9V-5W). I´m not sure that it will protect the devices because I don´t have specifications about it, neither “Absolute Maximum Ratings” nor Transient information (peak voltage vs Time, supported).
The devices current (400mA) is below the I-hold (500mA), and when a overvoltage appears the zener turns polyswitch on (I-trip = 1A) causing a Vz around 4.1V on the 3,3V power bus. I don´t know if 4,1 V is enough to protect it or I´ve to decrease this value!!!