NF-F12 , Nf-P12, NF-P14, and NF-A14/NF-A15 all have higher static pressure and are meant for restricted flow situations (filtered intake, HDD cages, heatsinks/rads)
Focused Flow is a NF-F12 specific thing http://www.noctua.at/main.php?show=focused_flow_system
If you look at the Silverstone Air penetrator AP121 they have the same claims and idea. It's more marketing than anything.
The main difference is the PWM IC on Noctuas is the only one known not to have any ticking noise, plus Noctua's NF-F12 uses VAD (Varying angular distance) to reduce stator vane noise on its NF-F12 , unlike the Silverstone.
If you're in Canada Id look into Be Quiet's Silent Wings 2 fan. At >900RPM it's quieter than Noctuas while cooling a few degrees better.
Our third favorite sounding model, the bequiet! Silent Wings 2, thankfully manages to hold its own, offering a strong balance of cooling proficiency and acoustic quality.
Gentle Typhoon Ap-14
http://www.silentpcreview.com/article1266-page5.htmlEdited by AlphaC - 8/9/13 at 4:47pm
The GT 1450 RPM model is also very quiet for its cooling peformance. The 19°C temperature rise at the 20 dBA SPL (at full speed) is comparable to what the big Thermalright 17cm can achieve at the same noise level. No other 120mm fan in this roundup does as well.
On paper, it scales down nicely, but there's a hidden flaw not shown in the SPL numbers: When slowed to any speed below ~1100 RPM, a sharp tonal spike around 500 Hz appears, and this is clearly audible at ~2 feet. It might be responsible for the slight 1 dBA increase at 900 Hz and below. I tried both of the 1450 RPM samples on hand and heard the same effect; ditto the 1800 RPM models. It also occured with both voltage controllers in the lab. Interestingly, at maximum speed, the tonal sound, a kind of ringing, could be triggered a bit by placing the fan on the wood lab table surface. Putting a soft pad under it eliminated it. This suggests it might be some kind of vibration-induced noise from the bearing, but the odd thing is that it is not apparent with the 800 RPM model.