SFL: Scythe 1200RPM nominal S-Flex, 7 blades
SS: Scythe 1200RPM nominal "M" Slipstream, 9 blades
NCB: GlobalWin NCB ceramic bearing 1300RPM nominal, 7 blades
Noc: Noctua 1300RPM nominal, 9 blades
MAG: Enermax Magma 1500RPM nominal, 9 blades
All fans are 120mm x 25.4mm ("25.4mm" is the complicated way Frenchmen spell 1"). Prop airflow sensor RPM was always 152RPM, SLM-hub distance 2.5", ambient ~30dBA. The fan voltage and RPM needed to provide 152RPM on the sensor prop are listed as well as the noise level at 2.5".
SFL 1006RPM 9.88V 36.8dBA
SS 1014RPM 6.73V 39.6dBA
NCB 1181RPM 9.86V 40.5dBA
Noc 1211RPM 10.04V 43.0dBA
MAG 1207RPM 6.98V 43.2dBA
In my earlier comparison of the SS and SFL, the S-Flex had to spin a lot faster to push the same airflow as the Slipstream. Here, with some backpressure, the two fans turn almost exactly the same RPM at the same airflow. This is why, although the SS wins in free air, SFL wins using this particular backpressure test.
Considering the NCB has been around a long time, is cheap, and has long-lasting ceramic bearings, I thought it did rather well. I've always liked that fan, and Madshrimps has adopted it as its standard fan for testing HSFs that mount 120mm fans.
Three of the fans were brand new out-of-the-box, and the other two were purchased recently and had only been tested once and not put to other use.
I've posted pics and info of the test fixture in the Silent Front forum, subject "A controlled back-Z fixture based on the HDT-S1283 HSF" if you want to know more about it.
edit: corrected "it's" to "its"