RealTemp takes a good stab in the dark at converting random sensor data into some meaningful temperature numbers but the exact temperature isn't that important. It's all pretty simple really. Run your CPU as cool as possible and the more you'll be able to reliably overclock it.

I learned the above fact during a Prime Small FFTs run on my E8400 C0 at 4050 MHz. It was running great for over 9 hours so I disconnected the CPU fan to see what would happen.





Core Temp was using TJMax=105C instead of 100C back then so you need to subtract 5C from that temperature.
I set SpeedFan to TJMax=95C which was also wrong so you need to add 5C to the numbers in that graph for the correct temperature.

It only took about 5 minutes for a nice stable Prime run to error out. At 58C, it was 100% stable. When the core temperature got up to 77C, it crapped out.

Core i7 can run reliably when overclocked to 4+GHz at over 90C. I found with Core 2 based chips that about 70C was the upper limit with a decent overclock. The harder you push, the cooler you'll have to run them to remain stable but I think most people here already know that.

The old "disconnect the CPU fan while running Prime Small FFTs" trick is a good way to find out how much temperature head room you really have and how stable your system really is.