http://www.digit-life.com/articles2/p4-throttling/index.html
Both started throttling around 75*C.
The system with a Prescott CPU shuts down at a higher temperature than that with a Northwood. The latter's peak was, in our case, 98°C, while Prescott never shut down at temperatures below 101°C, sometimes even working on at 105°C.
Both started throttling around 75*C.