People saying CFM does not matter is misleading.
The reason they say that is, it can move XX CFM at 0 pressure. Once you strap it to a case or a heatsink or something, you are adding pressure and slowing down the fan.
Fin shape and quantity, as well as fan casing thickness all help increase the amount of pressure the fan produces as well as the motor.
(If you have never done it, take a nice 120x38mm high CFM/Pressure fan and lay it blowing down on your desk, then plug it in and play some air hockey
)