I apologize Comp, I was misinterpreting the analog diode temperature with the IHS geometric center temperature.

According to Intel, the 67.9°C Thermal Specification for a Core i7-920 refers to the maximum Tcase temperature.

Thermal Specification: The thermal specification shown is the maximum case temperature at the maximum Thermal Design Power (TDP) value for that processor. It is measured at the geometric center on the topside of the processor integrated heat spreader.
In my opinion, this specification is directed at system builders that have the necessary resources to cut a groove in their IHS and correctly mount a calibrated thermocouple. That specification is not directed at the average end user for that reason. If an end user can't accurately measure Tcase then there's no easy way to determine if they are within this specification or not.

All Core i7 9xx variants:

Vcore Max 1.375v
Tcase Max (CPU temperature) 68c
Tjunction (Core temperature) 73c
Here's where I disagree. The Tcase specification temperature is not equivalent to the CPU temperature as reported from the Analog Diode. Your extensive testing has shown a 5C difference between the Analog Diode and the Tjunction based core temperature. In your example, you are now applying this 5C difference to the Tcase specification but your testing was based on measurements from the Analog diode. Tcase and Analog diode are not the same so this comparison or your recommended maximum Tjunction temperature is not valid.

With the introduction of core temperature digital thermal sensors, I don't think the data from the Analog Diode (what SpeedFan reports as CPU) has any relevance anymore. That reported temperature is not equivalent to a correctly measured Tcase temperature so you can't use this data to see if you are within the Thermal Specification. The CPU itself also does not use information from this sensor to determine thermal throttling or thermal shutdown. Both of those are determined by the core temperature.

Intel says:

Regardless of the configuration selected, PROCHOT# will always indicate the thermal status of the processor.
When the PROCHOT# signal is activated, the CPU will start to thermal throttle. After reading through a mountain of Intel documentation, that seems to be the only important thing to monitor or be concerned about.

If PROCHOT# has not been activated then your CPU is running at full speed and within the Intel design specification. That's why I included the reporting of that bit separately in the Thermal Status area of RealTemp. If this bit has not been set since power on, RealTemp will report OK. If your CPU gets too hot and the PROCHOT# signal is activated for even a millisecond, RealTemp reads this bit and will report it as LOG. That shows that at least one thermal throttling episode has been logged. If throttling the CPU by lowering the multiplier and lowering the core voltage isn't able to control the temperature of the processor then thermal throttling will be happening full time and RealTemp will report this as HOT in the Thermal Status area.

I think this quote really sums things up.
Thermal and Mechanical Design Guidelines
August 2008

4.2.6 System Considerations

A system designed to meet the thermal profile specification published in the processor datasheet greatly reduces the probability of real applications causing the thermal control circuit to activate under normal operating conditions. Systems that do not meet these specifications could be subject to more frequent activation of the thermal control circuit depending upon ambient air temperature and application power profile.

Moreover, if a system is significantly under designed, there is a risk that the Thermal Monitor feature will not be capable of reducing the processor power and temperature and the processor could shutdown and signal THERMTRIP#.
Intel wants computers designed so they are not tripping PROCHOT# or activating the thermal control circuit during normal usage so a user will be able to get the full rated speed out of their CPU.

The Tcase specification is designed to guide system builders. If they can design a computer and keep the measured IHS temperature below the Tcase specification then it is very unlikely during normal usage or even when running the most demanding applications like Prime95 or Linpack that the core temperature will ever get hot enough to trigger PROCHOT# and thermal throttling. If your measured Tcase temperature is 68C then even if a user is running Linpack and his peak core temperature is 30C beyond his Tcase temperature, the CPU will continue to operate at full speed and within specification because PROCHOT# will not have triggered.

(95c Tcase overtemp / 100c Tjunction Max) then the engine will shut down.
Just to be clear, a core temperature of 100C is not the thermal shutdown temperature (THERMTRIP#) of a Core CPU. The thermal shutdown temperature is approximately 25C beyond the typical 100C maximum junction temperature so thermal shutdown usually doesn't occur until a core temperature of 125C or even a couple of degrees higher during testing.

Thanks for explaining the Analog Diode / CPU temperature. I've never found this sensor very useful on my motherboard because of its calibration but now that I understand it better, maybe it will make some more sense.