Depends on the CPU completely! Ever CPU has it limits. Intel and AMD both publish the max temperatures the CPU could theoretically withstand, as well as recommend maximum operating temps for a particular model of CPU. Obviously AMD processors run hotter, and they had to engineer the fact that they were going to run hotter into the processor design, otherwise failure would occur very easily. Intel prides themselves on less current usage, and better thermal characterisitics, therefore most of their CPU's are not designed to handle the kind of heat AMD processers endure. This does not mean AMD processors are better because of the heat issue, but simply that Intel will not withstand the high temps. I would have to guess this is why AMD still uses a ceramic substrate to mount their cores into, and Intel uses a plastic epoxy. The ceramic will absorb some of the heat and assist in cooling, the plastic epoxy Intel uses is a very poor conductor and will force the CPU to retain most of its heat and transfer all of it to the heatsink, but since Intel processors displace less wattage, power, they run cooler. In the end, refer to manufacturers documentation for the real information on heat and power limits.
