I have use prime95 when CPU overclocking to stress test, and it does a great job. It won't hurt your CPU. That is kind of the point of it. Your CPU will shut down a core/s if it reaches thermal threshhold, and thats if you have disabled throttling. The other extreme, is if the CPU is not receiving enough power, it will stutter while doing a calculation and cause an error. Completely unharmful to the CPU, potentially fatal to data that may have been processing. Which is what we're testing for
...Once prime95 detects an error on a core, it kills the test on it.
It's one of those great applications that just does what it does, and does it well. Without the bells and whistles.