Alright so I have an i5 2500k CPU, a Asus P8Z68 V-PRO mobo, and a CM Hyper 212+ for cooling. To stress test I am using Prime95, CPU-Z, CPUID Hardware Monitor, and the sensor info on the AI suite too keep track of voltages and temperatures.
Now to overclock and adjust the voltages I am using the AI suite, that you can install from the asus website for their MOBO's. At first I used the auto tune feature on the program, and after 4.4GHz I would get temps above 70 degree celsius (like it would be a massive jump up to 70). Then I realized that the CPU voltage changed a lot, I noticed that past 4.4GHz the CPU was starting to pull in over 1.4 V which then kinda clued me in to what I was doing wrong.
So I've set my goal to overclock to 4.7 GHz, and it's pretty much all set. I've also successfully dropped my CPU voltage, so that if I stress test my CPU. It won't pull in more than 1.29V (rounded up number), which gives me maximum temperatures of ~63 degrees celsius.
But now I want to push the limits, and get the lowest possible stable voltages I can for this clock. But how will I know when I get there? and is there any risk from dropping the voltages too much?
If you use Prime95 to stress the CPU, it's easy to tell if you don't have enough CPU voltage -- your computer will reboot (with or without BSOD) or the program will generate errors. I recommend running Prime95 on the Blend setting for eight hours or more to test for a stable overclock. If it cannot run that, then it's not stable. I personally run Prime95 for 24 hours to test stability, but a lot of people don't have that kind of patience.
Unless you got very very very lucky in the CPU lottery, 1.29v is unlikely to be stable at 4.7GHz overclock. I hope I'm wrong though.
To keep a Sandy Bridge CPU happy for a long-term overclock:
1. Keep the peak Prime95 core temps below 75ºC
2. Keep the CPU voltage below 1.4v
Most people do not have that kind of patience. I'm a little more fanatical about stability. I run P95 small fft's to test the CPU and the blend test's for the memory. For a K chip, I would recommend using the small fft's test.
With an unlocked multiplier, the memory subsystem should not be a problem.