When I started this investigation I had some notion that there would be a large spread in cooling prowess between fans. I thought that most of my fan testing would be at 3.6GHz, and that only the best fans would cool my system at 4GHz. So much for expectations.
Conclusions:
1. Once you get to 1000 RPM or so, there is only about a 12c difference in cooling performance between the various fans.
2. As a practical matter, fans seem to max out between 2000 and 2500 RPM. After that you need huge increases in CFM to get another degree of cooling.
3. Although putting on a second fan helps, the amount it helps depends on the power of the first fan: the more powerful the fan, the less benefit you get from a second fan.
4. TANSTAAFL: By and large, if you want more air through your cooler, you will have to pay for it with more noise.
5. The blade count doesn’t seem to make much difference in cooling, but the depth of the fan does.
Do these conclusions sound obvious? Well, isn’t it nice when hard data supports conventional wisdom? The reality check goes both ways.
A few comments on specific fans:
The San Ace
9G1212H101(1) remains the Prince of Fans, at least on the Megahalems. One of these gives the best balance between sound pressure level and cooling performance.
And the Princesses of Fans: A pair of Yate Loon D12SH-12’s gives nearly the same cooling power with slightly less noise; but at the low voltages seen at idle, they will be quieter. Also, at US$7.40 for a pair, they are far cheaper than the $18.40 a US vendor wants for a single San Ace with bare wires.
Other worthy fans: CM Blade Master, Scythe Slipstream 1600’s, and the Japan Servo “square round†fan.
Some of the fans seem to have a higher SPL than perceived noise. Slip Streams do that, for example. So do Magmas. I would be very interested in seeing what a pair of Magmas can do.
So, what’s next? Do I test these fans at 3.6GHz on the same rig? Or do I mount a Noctua NH-D14 and see what 140mm fans can do in a cooler designed for them?
In the meantime, below are a number of posts arranged by brand that have more details on the fans, their specs and their performance, along with pics.
P.S. --
Here is what the TIM spread looked like. It was Gelid Solutions GC3 Extreme:

GC3 on the heatspreader. Fan direction was right to left (east > west).

Close up of GC3 on heatspreader. And no, I have no explanation for the dark lines in the middle. When the heatspreader is cleaned with Arcticlean 1 & 2, it doesn't show up.

GC3 on the heatsink. Sorry about the lack of focus.
You experts can tell me whether I had a good mount for an unlapped set of heatspreader and heatsink.
Bonus
How to mount fan clips on a Megahalems
Start with a Megahalems:
Now,
snag the lower screw hole with one end of the clip. Then
draw the clip back until the shaft of the clip
catches behind the corner of the fan clip groove:
A closeup of the catch:
Now pull the shaft up until it sits in the fan clip groove, then bring the end over to click into the top screw hole:
Done:
Edited by ehume - 10/28/10 at 10:51pm