If you are going to try out another fan, I'd hasten to suggest you look for one with deeper fins. They will provide a higher CFM at lower voltage and be quieter. For example, the stock NMB 4715KL fans that bitmain deploy are 1 inch (2.5 cm) deep, whereas a Nidec TA500DC is 1.5 inches (3.8 cm). If you can get a 2 inch deep fin / blade on the fan, I think you'll get an even better airflow + quieter for if you run them at less voltage.
PS. The Nidec TA500DC is not a 120mm fan, more like a 125mm fan, and on the S1's that I run it on, the holes do not fit those on the frame, however, it fits inside the frame and I attach them using double sided tape, that and the pull layout make it stick rather well. Additionally, I run them without the PWM (though they certainly have PWM as they are 6 wire). You can pick these off flea-bay for a pittance, shipped.
Umm.. not sure where you are getting your ideas from.
Its obvious just by looking at it that the S5 uses a 38mm fan, in fact the NMB 4715KL is a 38mm fan that pushes 130CFM@50dBA, not sure if thats what they are using on the S5 but nevertheless
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
Nidec TA500DC is a 127mm fan the 130CFM version is 48.8dBA and the 150CFM version 52.5dBA so not much in it.
The Silverstone is actually a better fan than both of them
Airflow: 42.8~171 CFM
Noise Level: 13.4~43.5 dBA(Max)
Even at max speed its more powerful than the Nidec and quieter than both, plus it uses the standard 120mm screw holes
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
Not saying its the best fan for the job, just that its not a bad one to try if you have it lying around from other stuff
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
Those are not ideas, they are the facts as I have them.
1. The NMB 4715KL has a 38mm frame BUT the fan blades / fins are, like I said, 25mm. I know this because I've just measured one. And it is classified as a 120mm fan.
2. The TA500DC has 50mm frame and the fan blades are 38mm, just like I said. It may indeed be classified as a 127mm fan (against my 125mm), but my point was that the holes on it will not fit a with the frame of an S1, and possibly S5.
I have no claims to make towards comparative noise levels, but like I suggested, I clipped mine with resistors to reduce the voltage / wattage and they work wonderfully with my OC's S1's with little noise, much better than the stock NMB 4715KL (even with the blue wire hack!). I put that down to the size of the fan blades.
And by the way, there is no speculation in my comment, and therefore no chance of confusing / mixing numbers like you did, just un-udulterated observation.