CompuTronix posted this nice Guide.
Intel's Thermal Specification (Tcase) for the i5 3570K is 67C, which is CPU temperature,
not Core temperature. Core temperature is 5C higher than CPU temperature due to sensor location, so Tcase +5 makes the corresponding Core temperature 72C.
This means that mid-70's are safe operating temperatures.
Throttle temperature is 105C.
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It's all explained in this Tom's Sticky:
Intel Temperature Guide -
http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html
" ... 3rd Generation 22 Nanometer: 3570K / 3770K (TDP 77W / Idle 4W)
Standard Ambient = 22C
Tcase (CPU temp) =
67C
CPU / Core offset + 5C
Tjunction (Core temp) =
72C
Tj Max (Throttle temp) =
105C ... "