CFM Ratings on fans are absolutely useless, even more so than monitor response time. Fans like any pump (a fan is essentially an air pump) have flow characteristics whereby flow changes with back pressure. So a fan may deliver:
90 cfm at 0.0 SP and 0 cfm at 1.20 SP. I may actually operate at 50 cfm @ 0.70 SP. Unfortunately there is no standard on how these figures might be presented and the most common leaves the impression that the fan can deliver 90 cfm at 1.20 SP.
Good Reading here:
"Why Static Pressure & Max Flow Specs Are Poor Measures of Fan Performance"
https://martinsliquidlab.wordpress.com/2013/02/18/why-static-pressure-max-flow-specs-are-poor-measures-of-fan-performance/
Which is the better fan ?
A. Cougar Vortex: Max Airflow = 70.5CFM / Static Pressure = 2.2 mm H20
B. Max Airflow = 58CFM / Static Pressure = 2.03mm H20
If you guessed A, you're wrong.