At first glance you probably won't notice that Reeven's Okeanos RC-1402 heatsink uses slightly different sized fans - a 120mm vaneaxial fan hanging off the front and a 140mm fan in between the two aluminum fin stacks. Using matched fans in a dual tower heatsink is always somewhat counter productive as the internal fan has to deal with the obstruction in front of it which negatively affects airflow and RPM. In the case of the Okeanos heatsink, both fans operate at nearly the same speed range, the 120mm unit rotating at 1800-300RPM and the 140mm PWM fan at 1700-300RPM.