You'll get more replies if you give some more info. Like:
CPU, speed, core voltage.
PC room temp, case temp and cpu temp under load.
Make and model of HeatSink & Fan (HSF) assembly.
Mid or Full tower case, what other fans already in it.
I have several Rotron "muffin" fans as well as some Sprites. They do a good job and are generally, not too loud. I don't use them as I'm not fond of 120VAC running around inside my case, not that it can't be done safely and effectively. If I did implement such a setup, I would use a DPDT relay, switched by the PSU +12 output. I would put it inside the PSU and buss it out to a terminal strip, along with a sub-minitaure toggle switch to manually disable the relay, shoulf I desire to do so.
Hoot