I agree with the post above about using spl values or temp rises maybe (delta T/SPL) as the independent variable. Other than that, great to see the FPM/CFM numbers, this helps balance out fans in a case. As you don't really want too much in the way of pressure in a case, too much negitive, and you pull in dust, too much positive and your fans don't move air well. There are very few small DC fans that handle high(few mm's of water, 1-3 inches are common in HVAC) pressures well. The other thing to point out about fans is that larger doesn't mean quieter even if the RPM goes down for the same amount of air. The tip speed(speed of the edges of the fan blades) may be higher, and the tips are what causes most of the noise, along with the trailing edges.
I wish heatsink manufacturers would provide pressure drop formula/curves, and Fan manufacturers would provide fan curves(rpm/power/cfm/pressure drop) then in your case it would be a relatively simple mater to test a heatsink. As a CPU is basically an electric resistance heater. You know the power in, you know the starting air conditions(temp/pressure/humidity), and the ending air conditions, so it's pretty simple to see how much energy you transferred to the air.
(wattage*3.413BTU/hr/watt) * Delta T * 1.08 = CFM
So if you vary the input wattage, and measure the amount of wattage disapated by the heatsink at a constant CFM, you can find out the maximum amount of energy that a heat sink can dissipate at that input air temp and CFM. This isn't very helpful unless you run the tests over a range of inlet temps, and CFMs. with enough points, you can figure out how an airflow change will effect cpu temp. It's way more work than is reasonable to expect, and i bet manufacturer already has this info. Getting it is a whole other matter.
Could you do FPM for PSU fans as well, preferably with the PSU case in place?
Same question as bozar. Is it true to say that :
Higher FPM at same SPL is better for a case fan (Noctua in lead)
Lower Â°C rise at same SPL is better for heatsink fan (Nexus in lead
I would say yes and no, really if you are going for quiet, then you want the lowest SPL that will move enough air in to dissipate the energy you need. You can think of a computer case as an electric resistive heater. You have an allowed temp rise,max operating temp of the components, with the worst case intake temp, so you need a set amount of air into the case to remove that heat. Now that you know how much air you need, you can find the lowest SPL that will move at least that much air, more air isn't a huge concern as that leads to lower temps. You will want some margin in there, as some of the air will simply be exhausted in most cases without cooling much of anything. So a higher FPM/SPL ratio isn't always better if you can get the FPM you need with a quieter fan. 30000FPM/100SPL isn't as good all the time as a 2000/50SPL, if the extra FPM is "wasted".
Sorry for the wall of text, the engineer in me is coming out. The big problem with most of the above is simply not having the data on the parts around, fan curves, pressure drop of the case. Thanks to SPCR we know roughly the efficiency of heatsinks(standard fan, and CPU/heater) so that helps.