Temps for stock cooler 3570k

Solution

IB's TJmax is 105C so 80C is perfectly fine.

An inexpensive HSF like the 212+ would likely bring that down in the neighborhood of 65C.

clutchc

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I couldn't find the max temp for the newer i5-3570k, but yours seems high. Intel rates the tCase temp at 67.4C. But I don't know how that relates to T/J Max temp. Personally, I would not run Prime95 for an extended period with a stock cooler.
 
The temperatures are fine but you can bring them down a good bit with a good 3rd party HSF. Like InvalidError said you can add the Cooler Master hyper 212 +/Evo bring the temperature down a good bit. Heck adding another 120mm fan to it can bring them down even more.