external probe on the side of CPU and the onboard thermal probe are both going to read low (unless you use an Asus then it may either be low or high depending on your cooling quality. If you are using a TBird to test blocks then I suggest you follow Joe's guide to epoxying a thermocouple under the center of the core. AMD has a technical pdf with an equation to relate that temp reading back to internal CPU temp:
Tdie = (1.209 * (Tceramic-Tamb)-1.3778) + Tamb
http://www.amd.com/us-en/assets/cont...docs/24228.pdf
Other than diode or the under socket thermocouple I don't think there is a good way to know CPU temp personally.