Retail SP120 PWM HP Dont Run at 2350RPM on H100i

Im just a little curious. About a month ago, I ordered the regular, non PWM SP120 High performance fans. Without the voltage regulator, they ran ~1600-2350RPM on my H100i. But when I returned them for the PWM versions, they only run at a max of 2050RPM



I currently have 4 SP120 PWM HP fans connected via H100i fan splitters for Push Pull in my 750D. How come they don't go above 2050, when they are rated at 2350RPM?