My iMac is wonderfully performant, but under extended load it sounds like a hive of angry bees.

I am using Turbo Boost Switcher to avoid using up all the CPU headroom, but for multithreaded applications it is not helping much. I would like to underclock the CPU (or GPU for that matter) to limit the heat produced.

In Windows (using Bootcamp) I found options for limiting CPU load in the OS scheduler (which is not exactly underclocking), and an option for limiting GPU power (making it "battery friendly").

Are there similar things on Mac? Are there ways to use the power controls to achieve something like this? My MacBook Pro also behaves this way when all cores are under load.