Noisy Dell 2850 fan replacement

[Infiltrator]

Hi There

I have a Dell 2850 rack server in my study rack with 6 Delta AFB0612EHE (standard dell) fans inside.  They are 60mmX60mmX38mm accordng to this datasheet I have found https://www.delta-fan.com/Download/Spec/AFB0612EHE-AF00.pdf

They quote a maximum dB rating of both 60 and 64 dB. Using a dB calculator and the worst case number, that would give me a total maximum dB rating of 71.77dB. http://www.sengpielaudio.com/calculator-spl30.htm

The average vaccume cleaner runs at 70dB so it explains why they are loud.

The Delta's run at 61.7 CFM (1.73m³/min) with a static pressure of 1.496 in H2O (372.6 Pa) at 11000 RPM.

I'm thinking of replacing all 6 with Noctua NF-A6x25's https://noctua.at/en/products/fan/nf-a6x25-pwm/specification

These are the questions I don't yet know the answers to.
#1, Have I read the datasheets correctly?
#2, The Noctua's are thinner, at 60mmx60mmx25mm, but they seem to fit into the bracket anyway.  Would this thinner size cause any issues like air leakage?  
#3 They seem to have a noise level of 19.3 dB giving me a total noise level of 27.07db down from 71.77db.  Does that seem right?
#4 The static pressure seems better at 2.18 mm H₂O vs 1.496 of the Delta's.
#5 the airflow 29,2 m³/h seems worse to me as unless I am doing something wrong, that would seem to calculate out to 17.2 CFM VS the delta's 61.7 CFM?
#6 the rotational speed seems much lower at 3000 RPM vs 11000 RPM. Now I can make adjustments in the Dell Openmanage software to set the fan warning levels?
#7 Is this just the wrong fan to replace my current fans with and is there a better choice than the Noctua.
 

Edited June 16, 2020 by Infiltrator
Font size standardisation.

[Infiltrator]

Yeah, there is a cabling job that needs to be done to the bracket, cutting and re-soldering wires into the connector but its not a big jb.

[Algebruh]

9 hours ago, Infiltrator said:

#4 The static pressure seems better at 2.18 mm H₂O vs 1.496 of the Delta's.

The static pressure of the Delta fan is 1.496 inchH₂O not 1.496 mmH₂O.

1.496 inchH₂O = 37.9984 mmH₂O.

9 hours ago, Infiltrator said:

#5 the airflow 29,2 m³/h seems worse to me as unless I am doing something wrong, that would seem to calculate out to 17.2 CFM VS the delta's 61.7 CFM?

44.5 CFM difference per fan, times 6, that's 267 CFM difference. (Assuming the CFM measurements are accurate.)

 

9 hours ago, Infiltrator said:

#7 Is this just the wrong fan to replace my current fans with and is there a better choice than the Noctua.

I dunno, the answer is pretty clear.