I found a few SPCR measurements, and found the sound sample page for the Nexus... and that makes me realize more than yes, the only way to really know what a fan sounds like in person, is to hear it in person.
If I'm able I might test a few fans, though I'd rather try to find a keeper and buy only that one. My guess is that with the help of this thread and the net the first fan will suit my fancy amicably.
I checked out the Noctua P12 and the Nexus. Both have some good numbers agreed by Noctua, xbitslab and spcr.
As a general benchmark, I'm using the sound level that is inaudible in a quiet room in a quiet house in a quiet neighborhood. Most sources online mark this at 20 dB.
xbitlabs seems to have a distinction for this.. "acoustic quiet", for their measurement of 33 dB. For SPCR, 19 dB seems to be a match for that same level, measured from 1m away.
(How SPCR defined the 19dB level (when testing Noctua NF-P12):
"Fan @ 7V: The fan was almost silent and very smooth. Close-up it was still audible, and the same airplane-type noise persisted though to a lesser degree.")
That dB level is the first criteria. Then the static pressure is next. Without really knowing what they mean, or what I'd like, I just look for the higher numbers.
Here is the condensed data & info...
Noctua NF-P12 (1300rpm)(12v)
L.N.A. ----- 1100rpm --- 9v --- >19 dB spcr
U.L.N.A. --- 900rpm --- 7v --- 1.2 mmH2O
-----Noctua -- 13 dB ---- 37 CFM --- (900rpm)
-----xbitlabs -- 33 db ---- 21 CFM --- (900rpm) (no voltage given)
-----spcr -----16 dB ----------------- (840rpm) = .6 mmH2O
home-measured the P12 (12v) at between 1-2 mmH2O
Nexus 120mm Real Silent (D12SL-12) - 36 CFM - 1.2 mmH2O --- (1080 rpm)(12v)
-----11.5v -- xbitlabs --33 dB --- 16.4 CFM - 1 mmH2O
--- (910rpm in tube)
-----9v ----- spcr ----- 19 dB --- 23 CFM --- .7 mm H2O
-----9v ----- xbitlabs -- 31 dB ---------------- .6 mmH2O ------- (750rpm in tube, 810 w/o)
xbitlabs in-tube and out of tube measurements give the apearance of discrepencies, but if SPCR is using out of tube, then the dB levels and the volt and rpm levels are in line.http://www.xbitlabs.com/articles/coolers/display/120mm-fan-roundup-1_10.html#sect0
spcr sound sampleshttp://www.nexustek.nl/NXS-nexus120mmrealsilentcasefan.htm
Pluses of the Noctua P12 are the use of a single simple included resistor to reach the desired dB level. However, taking it lower than 7v would require a fan controller.
Pluses of the Nexus are an apparent superiority of sound quality (from scanning comments all over), and that the desired dB is around 9-11.5v, so there's room to tune down more. Also it's $5.
Downside of the Nexus is that it'd require a fan controller (though the Zalman Fanmate 2 is about $5).
Another possible downside is the sleeve bearing: it couldn't be mounted horizontally, and I wonder how much heat the sleeve oil could handle?