I doubt I'll be going back to air from water cooling any time soon. I have Antec 620, though I got rid of the Antec fan (that was about as silent as a jet engine) and replaced it with a Scythe Gentle Typhoon that I hooked directly to a mobo fan connector. So, the speed is constant, not varying. My slightly overclocked Phenom II now idles at ~25 and goes up to the 45 you mentioned when fully stressed (Prime95). Though when gaming, the factory overclocked GTX 560 Ti effectively masks any other noise...