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
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
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
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.