This may or may not answer your questions, but thought I would post it anyway....
By design, 4 pin PWM fans are backwards compatible and will work with either a 3 pin MB fan header or voltage regulated (VR) fan controller. How well they work depends on the fan. I know from past experience that certain PWM fans do not work well or at all without a PWM control signal. The problem arises during startup. For example, using a PWM fan connected to a 3 pin MB fan header, the applied startup voltage (+VDC) off the fan header is ~12v. Most PWM fans can deal with this just fine... no problem. And after some time (usually after system startup) the voltage and fan speed is reduced based on some control signal like CPU temp. GPU fans are a good example of this... why they "rev up" during system startup.
On the other hand, using a PWM fan on a VR fan controller differ in that the individual channel controls (pots) may be set too low (or not compatible) for the fan to start up. Even when the voltage is increased, the fan will appear to start but just "pulse" back and forth. Other fans may not recognize "no PWM signal" present where 0% duty cycle = 0V, instead of +12V... and just sit there, growl and do nothing. Your comment about the noise issue when using PWM fans has some weight to it. Again, certain PWM fans deal with this ok.
Now, I know your are probably asking yourself isn't the Sunbeam Rheosmart a PWM controller?
Yes, it is but... it tricks 3 pin VR fans to operate like PWM fans, not the other way round. The only two lines on the output channels are ground and +12v. There are no PWM signals carried to any of the individual controller's output channels. If that were true, then you would see 4 pin fan connectors instead a 3 pin (actually 2 pin) and cost 2x as much!
So which controller you buy should not depend on whether its PWM, but rather... will my PWM fans work with it. Sorry again for the long post Edited by gymenii - 4/13/12 at 9:11pm