well that's just the thing, it outputs 80watts of heat, the tempurature of the hotside depends upon ow much you're cooling it, same as the temp on the cold side. if you dont use any cooling at all the whole thing will just get hot. so it's made to move 80 watts of heat. if you're cpu puts out 40 watts of hewat, that's more than enough to dissipate the cpus heat and bring it under ambient temp, if your cpu puts out 70 watts of heat, you gotta realize the contact points arent perfect conductors (cpu, coltplate, pelt, heatsink) even with a really good tim, so it will probably dissipate most of the heat, but if it cant keep up your processor will just get hot.
if you think of heat as a physical thing, and the pelt as a pump(which is what it is) you want to pump enough heat away from the cpu to keeop it cool. if the cpu produces mroe heat than the pump can handle it starts to overflow, just like pumping water out of a bucket that has water running into it