Despite what other people say, Handbreak WILL kill your system sooner or later , running that near the thermal limits for a long period will reduce the life of components around the CPU , and given that apples cases, whilst looking pretty, are not exactly optimum for heat dissipation other components such as the hard disk will also have its thermal limits pushed.
I use handbreak a lot, but i use it with a Process throttaling app, cutting handbreaks usage to 75% has the effect of keeping CPU temps in the high 60s - mid 70s instead of maxing out the thermal limts, and will extend the lifespan of all the other components hidden away in that case.
I have been saying for years that handbreaks devs should put in an option to manualy throttle back the apps CPU usuage, or even select the number of cores you want it to use. I would rather wait an extra 10 minutes for my encode to finish than have the inside of my device (macbook pro, imac, mac mini, whatever) hotter than the surface of the sun.
The MacPros (and PCs)have WAY better cooling than the rest of the mac range, and use desktop components rather than notebook components, i tend to find these are MUCH more forgiving and easiier to cool, but then having a huge chunk of metal the size of a mac mini for a heatsink on each CPU alone must help lol.