My best guess for Q6600 is:

Q6600 Stepping B3, TJMax=90C
Q6600 Stepping G0, TJMax=100C

Not even Intel publicly agrees with that opinion. They say that there is a TJ Target that they shoot for but actual TJMax might be a little different than that, usually higher.

The best test is to run your CPU underclocked at 1600 MHz and 1.10 volts and compare your reported core temperature to your room temperature near your heatsink with your case open. Your reported core temperature should be 5C or so above your room temperature. Check out the RealTemp docs at TechPowerUp for more info.