I have an Intel core i5 3570k, and stock cooling. I don't know if this is safe or accurate.
It's not accurate or safe? You didn't really answer the questions.
neither. It's not accurate because it's impossible to push a microprocessor's temperature below ambient without active cooling (cold plate, compressor, liquid nitrogen pot, helium, etc...). It's also not safe because TJ Max exists for a reason, to prevent damage. If you're getting close to it, you're running too hot.