OK, I've played around a bit with Fan Xpert+ now.
...but why is it spinning the fan at just 430-500 RPM?
Because with a cooler like the Mugen 3 the fan does not need to run any faster than that to keep the processor temperature stable.
While that may be true, I don't believe it's the reason
that Fan Xpert+ operates the CPU fan at 20% when idling. I think the reason has more to do with it assuming that the stock fan (which is what, 2000 or 3000 RPM?) is installed. That may be a reasonable assumption.
I'm still wondering about PWM control, though. When Fan Xpert+ is first run, it knows nothing about a fan's max RPM until the user manually runs a test at 100%. If that's true, then 20%, 50%, etc. are percentages of what
exactly? I can only assume that it's actually doing voltage control of the CPU fan rather than using PWM, at least until it knows what RPM 100% is.
I'm a little surprised that in Fan Xpert+ the fan profiles can't be spec'd in RPM, instead of percentages.