@Prebz: I hesitate to answer. It was a small tip and the cost saving is questionable. It does not warrant much attention under this forum topic and it has probably already had too much.
Here are the technical specifications on Arctic's website. (But take them with a pinch of salt):
P12 PWM PST
Fan Speed: 200 - 1800 rpm
Airflow: 56.3 CFM/ 95.7 m³/h
Static Pressure: 2,20 (mm/H2O)
Noise Level: 0.3 Sone
F12 PWM PST
Fan Speed: 230 - 1350 rpm
Airflow: 53 CFM/ 90.1 m³/h
Static Pressure: 1,00 (mm/H2O)
Noise Level: 0.3 Sone
P12 seems to give higher airflow and static pressure partly due to higher max RPM, but they are stating the same noise level. The noise level should presumably be at max RPM but that is not stated so it could be minimum RPM too. Apart from being insufficient information, there is no information about test conditions or even whether these are actually results from tests. Moreover, the actual installed conditions can dramatically change things, especially with noise and air flow.
Anyway, the Optimum Tech review that was originally linked in the original tip by Blub only talks about the Arctic P12, not the F12. It arose because people were highlighting the P12 as "cheapo" alternative to the Noctua NHA12x25 that performs almost as good. For the price though, don't expect the same consistency of performance or for them to last nearly as long in general.