The thing is, the higher your CPU temperatures are, the lifespan of your CPU will be shorter. That is why all strongly recommend to mount an aftermarket cooler even on stock settings processors.
You can use OCCT to stress test your CPU and monitor it's temperatures at full load as you gradually overclock it to 4.2 GHz (many people managed to do it and maintain it stable). It's your call to which speeds you want to overclock, you might as well read some guides about it over the internet.
Hope I helped here