LOL @ comparing Noctua to SilenX.
They make extremely good silent/quiet fans for those of us who prefer low noise to absolute best performance.
Obviously, there are fans out there that push a ton more air, but not w/o a ton more noise.
While you can get good cheap fans like Yate Loons, i don't like the YLs because they're a pain for easy cable management, whereas the Noctuas come beautifully sleeved already, not to mention the lower voltage adaptors they include for lower RPM saves one from having to manually mess w/ undervolting etc.
They might be pricey, but they're very high quality fans.
dampeal, after SPCR reviewed the NF-S12s & basically gave them #1 recommendation for silent yet good performance airflow, tons of people bought the Noctuas (myself included).
The biggest complaint made was that static pressure wasn't as good, therefore rendering it slightly less than the best for use blowing thru very tight spaces like heatsink fins, certain case vent, etc.
They mention how they address that here:
http://www.noctua.at/main.php?..._p12_comparison&lng=en
When i can find a CND e-tailer with them in stock, i'll likely pick some up...see if they do any better with my Ultra 12 eX than the NF-S12s.