Here's the formula that all software uses:

Reported Temperature = TJMax - Digital Thermal Sensor reading

All software reads the same data from the same on chip digital thermal sensors. The disagreement is in TJMax. RealTemp and Core Temp assume that value is 100C and other software assumes that value is 95C so RT and CT will always report a temperature 5C higher than the other programs.

Which value is correct? The truth is that there is no documented correct value. All software is guessing.

The only documentation ever published by Intel calls this value TJ target and they've said that this is not a fixed value. It can and does vary from one CPU to the next with the same model number and in my testing it also varies from core to core on the same CPU. Your core 1 reading much lower than the other 3 is a good indication of that.

These sensors are designed for thermal throttling and thermal shut down control and are accurate enough for those purposes. For any other purpose like accurate temperature reporting, the 45nm Core 2 Duo/Quad sensors are crap with a long list of known issues. 100% accurate temperatures from these undocumented sensors from idle to TJMax is simply not possible.

If you want RealTemp and Core Temp to low ball your temperature readings like the other programs are doing then set TJMax to 95 instead of 100.