To address concerns about pressure...
Given fans of 25mm depth spinning at typically <1500rpm, the pressure is always very low, and differences between models is trivial. To wit -- we have interchanged Nexus, Scythe, and Globe 120x25mm fans running inaudibly on Ninja HS with no significant differences in cooling. I've done the same with 80x25mm Panaflo, Nexus and other fans on earlier HS -- again without any notable change in temperature.
No, we have not confirmed it with an empirical experiment, but we will.
People should remember why HS like the Ninja are favored here: Low impedance. It means a low airflow, low pressure fan can work very well.
The reason for the absence of pressure differences has to do with the thin depth -- 25mm. The blades cannot have enough depth for any to exhibit real differences.
I quote from http://www.acal-radiatron.com/fanselection.php
Static pressure increases exponentially with airflow. So the actual cooling system operating point is where the plot of a prototype system measurements intersects the fan performance curve, and designers should aim to select a fan where this falls within the â€˜sweet spotâ€™ area.
This is if you want the best cooling/noise ratio. It's my contention that given a specific size 25mm depth fan, you hardly need to consider cooling -- they will almost all be the same at the same rpm. It's the noise that really differs.
Why are there so many different fans?
Fans can be provided for a wide range of voltages, including DC & AC, from 25mm through to 254mm square frames although AC types are usually limited to fans 80mm square, and larger. Clearly a wide range of operating voltages simplifies matching the fan to existing power supplies, for example Micronel offer a 80mm fan with a unique 5V option, while Airflow Tech offer both 48 and 53 V DC models. Apart from considerations of supply voltage, the three key physical parameters are:
1. Frame size
Larger frame size and higher fan speed generally increase airflow, but since higher speed also creates more pressure and noise, the optimum selection will depend on a balance between space available and acceptable noise levels. It is worth noting, however, that it can be difficult to achieve high reliability within the smallest of frame sizes not least because of the lack of space for adequately sized ball bearings (ie less than 10mm thick usually results in very high loading).
The thickness of the fan determines its pressure capability, but note that the datasheet pressure rating is for stalled air (i.e. no airflow), so it is important to check the performance curve to find the airflow delivered under your expected system static pressure conditions. All other things being equal selecting a thicker, and so higher pressure rated fan will normally deliver more airflow against a given system pressure and this may be a more practical alternative for increasing the effective cooling than fitting a higher speed or a larger framed fan.