Doing some research on the temperature issue. For stock speeds, I have found this document:
Page 77: Thermal Profile (Intel® Core™ Duo Desktop Processor E6000 Sequence with 4 MB L2 Cache - Thus the E6600 & E6700).
Formula: Tc(MAX) = 0.26 x Power(W) + 43.2. Since the maximum specified power is 65W, Tc(MAX) = 0.26 x 65 + 43.2 = 60.1C. The cardinal question is now, how far this relationship between power and temperature can be extrapolated. Obviously, Intel is not going to specify anything beyond stock specs.
From same document, we see that the Tc(MAX) for the E6300 & E6400 is a little higher, as defined by Tc(MAX) = 0.28 x Power(W) + 43.2, thus 61.4C @ 65W power.
Finally, the Tc(MAX) for the X6800 is 0.23 x Power(W) + 43.2, and the X6800 has a max specified power of 75W, translating into a Tc(MAX) of 60.4C.
Again, this is all at stock Intel specifications. I will try to find how far the lineair relationship between power and Tc(MAX) can be extrapolated (if any) and if there is a definate answer to the question what the absolute safe Tc(MAX) is.
And indeed, these temperatures are defined at the geometric top center of the processor. TAT and Core Temp measure the individual cores, and thus spit out higher temperatures.