http://www.xbitlabs.com/articles/cpu/print/p4-temp.html
That is a good article explaining the ALU temp diode and its function on the P4.
Quote
"Intel claims that the integrated thermal diodes are calibrated specifically for each given CPU on the manufacturing stage" End quote
So as we see, each diode is calibrated differently for each cpu to match against an equally unique "critical value" for each cpu. I do not see them being good comparative values from cpu to cpu for test benching.