Of course when it comes to air flow, its not only the heat sink's fan that will matter. Whatever needs to be done to get a decent airflow around the case and around the HSF will work best.
In other words, 50cfm fan on an Alpha won't do much good if you don't have a case fan.
120mm 50+cfm drawing in, 38cfm GW fan on an Alpha, 80mm fan sucking from the CPU, plus PS fan seems to do a good job. Can't seem to get my CPU above 40C anymore.