Thank you for contacting Intel Communities.
I understand that you changed the voltage of your CPU at BIOS level and you would like to know if it may have been affected.
If you would like to test your processor, there is a tool from Intel called Intel® Processor Diagnostic Tool; you can run its tests to see if any component of your CPU has been affected.
If this happened for a short period of time, your CPU should not have been harmed or damaged.
Most stress test would cause high temps in your processor, it would take it to its limits and higher which would be the reason why overheating may be present.
The TDP for the Intel® Core™ i7-4790K Processor is 74.04°C, any temperature under that would be secure.
Intel® Processor Diagnostic Tool links:
More information about Intel® Core™ i7-4790K overheating:
Do not hesitate to advise us if you have any additional questions or concerns.