the left top fan is a Noiseblocker BlackSilentPro PE-P 92mm. the right one is a Noctua NF-B9 PWM.
I would say the noctua is quiter, but it is hard to say cause there is not that much difference at all.
I'd guess both fans are running at full speed as they are connected to the BFL Single.
Sorry, I meant what bitstream(s) are they running?
(Guess it doesn't really matter since I ordered 6 of the Noctuas yesterday...)