I am wondering which Scythe case fan is better between the following two series:

Slip Stream 120mm Case Fan
http://www.scythe-usa.com/product/acc/0 ... etail.html

Slip Stream Kazemaru2 140mm case fan (120mm mounting holes)
http://www.scythe-usa.com/product/acc/1 ... etail.html

If I am understanding the specs right, those 140mm fans are similar or not as good as the 120mm fans... am I right? (I was expecting same airflow with less noise from 140mm fan vs 120mm)

Comparing the 1200 rpm models: (the ones Im most interested in)
120mm fan produces 24.00 dBA and 68.54CFM
140mm fan produces 23.20 dBA and 65.2CFM

Comparing 1700/1900 rpm:
120mm @ 1,900 rpm = 37.00 dBA and 110.31CFM
140mm @ 1,700 rpm = 36.40 dBA and 92.4CFM (same noise but a lot less airflow = a lot worse than the 120mm when you'd expect a 140mm to perform better)

and the slower 140mm fans produce a bit more airflow with significantly more noise....

Is there something I am missing in all these specs, and is there any reason/advantage to get the 140mm fan over the 120mm? (both use the same 120mm mounting holes).

EDIT: I've taken a look at the newer Glide Stream series, and it seems to have similar results... the 120mm fans push more air quieter than the 140mm fans, and do so with higher static pressure. Note that Im going by the test results, not by the manufacturer stated specs. It seems there is absolutely no reason to get 140mm Scythe case fans... they perform poorer than their 120mm counterparts.
http://www.coolingtechnique.com/recensioni/74/1136.html (translate with Google Translate).

In my experience, the 140 mm Slip Stream fans are not as smooth as the 120 mm versions. I use 120 mm 500 rpm Slip Streams as case fans and a pair of 140 mm PWM Slip Streams on my CPU cooler. Compared at 500 rpm, the larger fan sounds slightly rougher, but both are obviously very quiet at this speed. At high speeds (above 1000 rpm; higher than they ever reach in my system) the 140s have some tonality - more, I suspect, than would the 120s. The struts are nicely curved on the 120s, on the 140s they're straight.

The Glide Stream series has curved struts in both sizes, so the 140 mm versions might not be 'handicapped' the way the 140 mm Slip Streams seem to be. I haven't heard a Glide Stream fan in action, but they look promising.

Thanks for your input!

This will help me choose the right fans for my case.... I will probably be buying some fans after New Year's Day.... I will make sure I post my impressions whatever I end up getting.

Okay... I bought a single 120mm Scythe Slip Stream fan. I got the PWM Adjustable version for which Scythe states: "Speed of this fan variation is continuously adjustable between 470 (± 30%) to 1,340 rpm (± 10%) and 740 (± 25%) to 1,900 rpm (± 10%)."

My case's side panel has an area for two 120mm fans, but the mesh was simply making the fan way way too loud, and totally killing airflow. So I cut out the mesh and now there is just a hole there. The fan is totally free to push air now. Its a lot quieter and pushes way more air.

Today I upgraded my power supply (because it was the loudest component in my system) to something quieter than what I had. I got the Seasonic S12II-520Bronze.
After the upgrade the two fans that came with my Spire Sonex case (800 rpm) were audible.... so I disconnected those totally (Ill replace them with something quieter later).

This is where the Scythe Slip Stream that I bought comes in. In my system, I need to take it down to about 600rpm for it to be inaudible. At this level, my 7200rpm Samsung Spinpoint F3 hard drive (which I have suspended to reduce vibrations) is the loudest component in the system.

To anyone who is a first time buyer of various case fans and is wondering which Scythe Slip Stream is "quiet" or not, and which speeds they would set their fans to for idle or load, let me give my impressions. (others may disagree, as I said, these are my impressions, feel free to add your own comments).

At 1,900 rpm the 120mm Slip Stream is damn loud! They rate the fan at 37dBA. To most this is quite obvious, but to some, including me, "37dBA" means nothing until you actually hear it. Only then do you have a comparison point for the other fans and decibel levels. At this noise level it will by far be the noisiest fan in an already noisy PC.

At 1,200 rpm the Slip Stream is probably as loud as most people ever want their PC to get under full load, and still too loud for idle. Depending on the other components in your system it may or may not be the loudest component, but will still be quite audible.

At 800 rpm I would call it quiet for most people who do not have especially quiet PCs. At 800 rpm you wont hear the case fans above the other stuff in your computer.

At 600 rpm its inaudible in my current PC where my suspended hard drive is the loudest component when idling.

I cannot comment below this noise level.

Since I am overclocking my cpu, and plan on upgrading both my cpu and graphics card to higher TDP models and overclocking them as well, I will probably end up getting 1200 rpm Slip Streams and putting them on a fan controller. If I had to stick with a fixed rpm Slip Stream, I would not get anything over 800 rpm.

My case fan setup will probably end up being: 4 x 120mm case fans total
2 x 1900 rpm PWM adjustable fans for the side panel (adjusted to inaudible at idle).... (or my current 1900 rpm fan and buy a 1300rpm pwm fan)
2 x 1200 rpm fans for front intake and rear exhaust on a fan controller (adjusted to inaudible at idle)

My 500 rpm Slip Streams are closer to 600 rpm at full speed (somehow SPCR clocked it at only 440 rpm at 12 V), and slowing the intake fans made my system noticeably quieter until they dipped below 500 rpm, but at 7200 rpm your HDD is probably somewhat noisier than mine...

My personal maximal threshold for fan speed (I own a Scythe Slipstream 800rpm), is ~500 rpm. My harddrive is turned off completely when idle, so it's quite reasonable that your threshold is a bit higher than mine.

Well, previously I suspended my hard drive with wires, but they also conducted some vibrations to the case. This time I did it properly with white elastics and the noise level has slightly dropped.

I have added a second PWM Adjustable Slip Stream to my side panel, and I can now say that at 600rpm, both fans spinning are slightly audible. However, without a spinning hard drive (or a quieter hard drive), your systems are certainly quieter.

I might even re-think my current setup by simply adding two 500 rpm Slip Streams to my case (front intake and rear exhaust), and have them on all the time. (instead of 2 x 1200rpm Slip Streams on a fan controller adjusted to 'silent' speeds).
These would be silent. When needed I could turn on the two side panel PWM fans. This way I do not need a fan controller.