You should probably be looking at CFM (cubic feet per minute) which is the measure of how much air is pushed through, and static pressure which is the the pressure at which the fan pushes the air. Higher RPM may mean more airflow but also more noise. The same could go with high CFM, but since you are looking for PWM fans it should be alright. Radiators typically will favour high static pressure fans.
EDIT: Also for radiators, you should be looking at SP fans not AF fans. They should have a white LED variant for the SP140.