Did anything become of this? Is there a quieter, variable fan? In an Antec Three Hundred, it's loud enough that I can hear the annoying variation in speed whenever there's the slightest CPU activity. I don't know why it has to react so quickly, but it does.
Is there a quieter, variable fan?
A fixed speed Nexus undervolted to about 800 rpm will be quiet and do a good job of moving air.
PWM fans seem to be louder than non-PWM fans and some people are annoyed, like you, about speed variation. I don't think SPCR has ever identified a PWM fan as good as a non-pwm fan. Maybe this will change, Mike tells me that SPCR is about to publish a new set of fan tests.
One hopeful sign is the Noctua has just started to sell a new line of PWM fans. I'm sort of hoping that these might end up being good PWM fans.