This site is very usefull when it comes to searching silent hardware.
And maybe I got an idea what gives just a little bit more precise information regarding the reviews:
I've stumbled per accident into an article on wikipedia about the dB(A) weighting. It's a measurement for the loudness of noise corrected for the human ear. It's a fact that equal dB's can be experienced as beingg different in loudness. That's because the frequency of the noise is different. When (also) the dB(A) weighting is also reviewed, we can precisely define which hardware-part is more quiet.

AFAIK dBA's are already used by SPCR, just read a review and notice the noise measurement units.

Yes, all SPCR results in the reviews are dBA weighted. As for some of the posts in the forums...that's anyone's guess.