Back when AMD64 was relatively new I had a case with various case fans which I could control. The machine ran Linux. I controlled the fans by hand with knobs.

Back when AMD64 was relatively new I had a case with various case fans which I could control. The machine ran Linux. I controlled the fans by hand with knobs. I know this isn't what you meant but what's inherently bad for this if its a PC you have physical access to? What I did was put the fans down when I went to sleep. Its not like you can change power profiles dynamically, only on remote computers software controlled is better. And if its remote machines, who cares about the noise?