OK, Well That Was Emotional
My computer is now working at 5Ghz, 24/7.
Overclocking a Sandy Bridge (i5-2500K) CPU is completely different from any other type of CPU I have ever done.
In short (to save yourself a lot of heartache) here is the recipe:
1 - Leave all of the CPU power features ON, turn off the turbo setting. Disable Spread Spectrum.
2 - Set your RAM to its specified speed and voltage.
3 - Increase your multiplier to 50.
4 - Increase your VCore to 1.4 volts (mine is 1.44V)
5 - Get a really good cooler cause it will get hot. And if it gets too hot it will throttle down to 2.shit Ghz and remain hot. But it wont fail (!).
Thats it! Even in Turbo mode, the core clocks down to 1.6Ghz when idle, and my temps sit around 20-25Degrees in idle! Under load (@5Ghz) Coretemp maxed at 69Degrees then stabilised. I havent given it a burn-in yet, its only been on for a couple of hours. Im using this cooler:
http://images.esellerpro.com/2272/I/135/61/mugen%202%20ebay%20logo.jpg
The fan is a 120mm fan to give an idea of scale. I have 2 fans on my cooler, one is at 100% permanently.
End log.