In case you ever do want better quality fans, Scythe S-Flex and Gentle Typhoon fans are generally regarded as the best fans for radiators due to their quietness/high static pressure/long lasting bearings.
Fan Testing Part 2 (Retesting + Noise) - XtremeSystems Forums
It's pretty linear actually, for any CFM.like i said on another thread, anything over 75cfm get exponentially louder with diminishing returns.
Fan Testing Part 2 (Retesting + Noise) - XtremeSystems Forums