Here's an interesting thought, confirmed through personal experience.
Some fans -- such as that which you mentioned -- do not come equipped with speed monitoring (the yellow wire).
Yet, connecting such a fan to the CPU_FAN header of your motherboard will still allow you to vary the speed with software like SpeedFan. Speedfan allows you to set the minimum fan speed at a percentage of the maximum value. If the maximum value is accurately reported by the manufacturer of a fan without rpm monitoring, setting the minimum value with SpeedFan simply changes the voltage or pulse-width-modulation of voltage, and you should be comfortable knowing the approximate minimum fan-speed setting by multiplying the chosen percentage value by the rated maximum fan-speed.