Maximum fan speed?

[Cris70]

Hi all,
I own a TS-251+. Today I had some problems with high temperatures, so I looked at the fan speed.
My fan is spinning at around 1450-1480 RPM. It is set to spin at maximum velocity if the NAS temperature goes over 50°C (I'm at 52°C presently).
I don't understand if the fan is behaving correctly, as I don't have historical data about its speed.
Do you know if this fan is supposed to reach a higher speed, or if it's supposed to spin at around 1450 when at full gear?
It seems slow to me (and it's very quiet), but I don't really have any idea so I'm asking.
I haven't been able to find anything (regarding maximum RPM) by Googling around.

Best regards
Cris