OK, lets make it more insteresting then.
Lets say I had 5 of these fans that were controlled by the onboard monitoring software and didn't run at full pace normally.
Add to that 2 x fans that draw 1.2A as well
Given the above situation, what rating of potentiometer would you buy to slow these fans down, (In fairness I probably don't want them at half speed just probably UP to half speed so that I can have a play around with the noise/temperature levels.)