Not safe to use Prime95 v28.5 with 4790K?

never heard about that , but you can use aida extreme anyways

Recent versions of Prime95 aren't recommended for Haswell and later Intel CPUs because they run AVX instructions on the FPU that leads to unrealistically high temperatures. Prime95 Version 26.6 is the last version that didn't do that and can be safe to use on newer Intel CPUs, but won't test AVX at all.

As such you're better off using other testing utilities like Intel Burn Test, OCCT or Aida64 if you want to stress test your CPU.

Supernova1138,

There's a difference between Stress testing and Thermal testing.

Guys,

The only proper way to Thermal test your Core temperatures is to use a STEADY-STATE 100% workload that will run your processor as close to 100% TDP (Thermal Design Power) as possible. That's what Prime95 v26.6 Small FFT's does.

A Steady-State workload produces Steady-State temperatures, which is the best method to get accurate thermal measurements.

Fluctuating workloads produce fluctuating temperatures, which is not the way to go. Take a look:

Section 13 - Thermal Testing @ 100% Workload

Prime95 Small FFT's is the standard for CPU thermal testing, because it's a steady-state 100% workload. This is the test that Real Temp uses to test sensors. Version 26.6 is well suited to all Core i and Core 2 variants.

Core i 2nd through 6th Generation CPU's have AVX (Advanced Vector Extension) instruction sets. Recent versions of Prime95 such as 28.5 run AVX code on the Floating Point Unit (FPU) math coprocessor, which produces unrealistically high temperatures. The FPU test in the utility AIDA64 shows similar results.

Prime95 v26.6 produces temperatures on 3rd through 6th Generation processors more consistent with 2nd Generation, which also have AVX instructions, but do not suffer from thermal extremes due to having a soldered Integrated Heat Spreader and a significantly larger Die.

Note: If you overclock and run applications which use AVX, you may need to reduce Vcore and clock speed and / or upgrade your cooling so that Core temperatures don’t exceed 80C.

Prime95's default test, Blend, is a cyclic workload for testing memory stability, and Large FFT's combines CPU and memory tests. As such, Blend and Large FFT's both have cyclic workloads which aren’t suitable for CPU thermal testing.

Other stability tests such as Linpack and Intel Burn Test have cycles that peak at 110% workload, which again aren’t suitable for CPU thermal testing. The test utility OCCT runs elements of Linpack and Prime95, but will terminate the CPU tests at 85C.

The "Charts" in SpeedFan span 13 minutes, and show how each test creates different thermal signatures.

Shown above from left to right: Small FFT's, Blend, Linpack and Intel Burn Test.

Note the steady-state thermal signatures of Small FFT's, which allows accurate measurements of Core temperatures.

Shown above from left to right: Small FFT's, Intel Extreme Tuning Utility CPU Test, and AIDA64 CPU Test.

Intel Extreme Tuning Utility is also a cyclic workload. Although AIDA64's CPU test is steady-state, the workload is well below Thermal Design Power (TDP), which is insufficient.

CT