I second the S-Flex. They are about even with the Noctua P12's, but when some restriction is put on the airflow (radiator, heatsink, etc) the S-Flex pulls ahead. But, if you don't mind some noise, there are many extremely powerful 38mm thick fans that will provide lots of airflow and pressure, but they are loud. If you can find it, the San Ace H1101 is probably the best fan out of all high speed fans (high speed bing 100-130CFM), but it is nearly impossible to find and costs around $20-25.
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