LOL... wow didn't expect that from you, but let the lesson begin:
static pressure.
some fans blow less CFM but have a higher static pressure...
In this case its blade design and fan thickness that affects static pressure. A 50 CFM 25mm fan will get killed by a 50 CFM 38mm fan if you put it on a heatsink, because the 38MM is less susceptible to the backfeed and the restriction of the cooler, and actually blows
MORE air THROUGH the heatsink.
This same concept applies to fan design and blade orientation/spacing of fans using the same thickness.
so:
Noctua NF-P12
http://img.techpowerup.org/100328/stock.jpg
and
Noctua NF-S12
http://img.techpowerup.org/100328/noctua_nf_s12_1.jpg
The top has more pressure, and is better on heatsinks even at lower RPM, even noctua will tell you this:
http://noctua.at/main.php?show=nf_s12_p12_comparison&lng=en
Same with water pumps, some pumps dont have the GPH of others, but have a higher head pressure due to to motor and impeller design.
here is some bathroom reading:
http://www.overclock3d.net/reviews/cases_cooling/noctua_nf-p12_static_pressure_performance/1
"The new Noctua NF-P12 now provides the static pressure needed for both heat exchanger and heat sink applications. All credit goes to Noctua for stepping up to the plate and making an even better product than the NF-S12's. Equally impressive is that you can now 'have your pie and eat it too' - cooling performance without the additional noise.
Subsequently, I have absolutely no hesitation in recommending the Noctua NF-P12 120mm cooling fans as a worthy addition to your cooling system."
so... this is why its always a good idea to
know the tech specs of a product before relying on one
Standard to measure performance. I know that you know better, or should know better, you wouldn't judge a PSU based on WATT rating alone.