5V ultrasonic device on Arduino, might've broken non-5V tolerant wireless module

fungus:

arusr:
If I'm not mistaken, the voltage/frequency spec is for the quoted operating temperature, up to 85C. If you don't use it in that hot an environment, you can get away with overclocking it.

Where does it say that on the datasheet?

Assumption on my part. It doesn't make sense to that the reliability is the same across the entire operating range of operating temperature for the same voltage/frequency combination.