The two motors are (to the best of my knowledge) essentially identical. There was some controversy over things a while back.
This is not a good rule of thumb, and I will explain why.
This is a wonderful resource: https://motors.vex.com/
Specifically the 775Pro Data here: https://motors.vex.com/vexpro-motors/775pro
This is a locked rotor stall test. From this data we can see that there are some voltages where the motor can be stalled nearly indefinitely. Even at 6V (roughly 50% command throttle) the motor could survive a whole FRC match. Last year many teams, including mine, stalled 775Pros to hold mechanism position with no noticable performance degradation over the course of a season.
If, however, the motor is stalled near full voltage, expect to let the magic smoke out in a small number of seconds.