I'm seeing forums with people saying its 80c. On the manufacturers site they say its 72c. What is safe?
They're correct ... 80°C. Although Intel's Product Specifications website for the i7 4770 shows "Tcase" as 72°C, it's not quite that simple. Tcase is not clearly defined for users, so it's frequently misinterpreted, poorly understood and misleading; thus your question reflects the confusion Tcase causes within the community.
Intel doesn't tell you that Tcase is a factory only measurement that you can't monitor. They also don't tell you that Tcase is not the thermal limit, nor do they tell you that Tcase is not Core temperature. After 6th Generation, Intel stopped using "Tcase" as a Thermal Specification, and instead now uses "Tjunction".
Tjunction (Tj Max) or "Throttle" temperature for the 4770 and 4790 is 100°C. This specification is not on the Product Specifications website for your CPU; it's instead shown on Intel's 4th Generation Datasheet:
See page 76, Table 27, second row, fourth column; TCC Activation Temperature.
This is the absolute Core temperature limit where the processor will automatically throttle (reduce Core speed and voltage) to prevent thermal damage. Since cooler is better for ultimate stability, performance and longevity, it's prudent to observe a reasonable thermal margin below Tj Max.
Core temperatures above 85°C are not recommended.
Core temperatures below 80°C are ideal.
Here's the nominal operating range for Core temperature:
Intel Desktop processors have temperatures for each "Core" and a temperature for the entire "CPU". Core temperatures are measured at the heat sources near the transistor "Junctions" inside each Core where temperatures are highest. CPU temperature is instead a single measurement centered on the external surface of the CPU's "Case" or "IHS" (Integrated Heat Spreader) where the cooler is seated.
Core temperature is considerably higher than CPU temperature due to differences in the proximity of sensors to heat sources.
Intel Desktop processors have two Thermal Specifications. For Core temperature it's "Tjunction" which is also called "Tj Max" (Temperature Junction Maximum) or “Throttle” temperature. For CPU temperature it's "Tcase" (Temperature Case) which is a factory only measurement.
Both Thermal Specifications are shown in Intel’s Datasheets which includes definitions, technical descriptions and more. However, Intel's Product Specifications website is a quick reference that shows Tjunction (Tj Max) for 7th Generation and later processors, or Tcase for 6th Generation and earlier.
Tcase has always been a confusing specification. Here's why:
When users of 6th Generation and earlier processors see their Thermal Specification at Intel’s Product Specifications website, most don’t realize what Tcase actually means. Since there are numerous software utilities for monitoring Core temperature, users assume Tcase must be maximum Core temperature. This is a basic misconception which has persisted since 2006.
Tcase is not Core temperature.
Intel defines Tcase as “the maximum temperature allowed at the processor’s Integrated Heat Spreader (IHS)”. Users can't monitor IHS temperature; it's a factory only measurement.
Intel defines Tjunction as “the maximum temperature allowed at the processor’s Die”. The “Die” contains the Cores, where the highest temperatures are measured near the transistor Junctions.
Since Core temperatures can be monitored by users, but IHS temperature (Tcase) can't, Core temperature is the standard for thermal measurement. Accordingly, Tjunction (Tj Max) or "Throttle" temperature is the limiting Thermal Specification; not Tcase. As such, Tcase is an irrelevant specification.