Yeah its a bit nuts with the number of fans on it... and its also not entirely accurate to compare fans based on RPM, as some fans blow more air at the same RPM.... although, as a crude generalisation it works.
Given the topic of this particular forum, this graph is probably most useful:
Given we want the lowest possible noise and the highest possible air flow, we want fans which are in the upper left corner of that graph (low noise, high air flow). Each fan is measured at different speeds, which obviously affects both factors, hence the line.
The gentle typhoons (brown filled square) are excellent based on that information.
All the usual testing caveats apply here, especially as I doubt Martin's equipment is on the same level as SPCR's... however, it does provide an interesting comparison of fans.... not to mention videos to listen to. The reason videos are good is that pure dB doesn't actually give you an idea of how annoying the sound will be. The other thing to note, is that the two different gentle typhoon fans tested are slightly different... whether this is due to testing inaccuracies or quality variances I cannot say. They do both test pretty well tho!
EDIT: The reason I included the other graph above is that when you buy fans, you buy xxx rpm...
EDIT2: If you don't read anything else from Martin's report, this is important to note:
-Motor noise is generally smoother the smaller the fan motor hub, but also a higher pitch. 38mm fans with the extra large fan hub general have more of a pulsing or motor ticking type of sound when running very low rpm levels. This measures low from a dB standpoint, but it's a noise that many may not like...you really need to listen to the videos to see that.
-Noise tone and quality often times varies across the voltage range, sometimes it can even get worse at one voltage and get better with a higher voltage, it's one of those sound dynamics that occurs.
-Fan generally produce more CFM per RPM the thicker the are, the more curved the blade, and the more number of blades.
-There is no consistency between fan families. I've seen several cases where the same series of fan has very different sound responses, you simply can't depend on consistency there.
-It gets really really hard to choose between fans in the ultra silent 1000 or less category. My instruments were simply not able to measure CFM levels that low and to my ears, they are all silent down at that level.