Here's one for you. When I build a new system, I always end up using air-cooling and heatpipes, so I try and pressurize the case and force all the air through the CPU cooler (with an exception of a second exhaust in some instances, but that's another topic).
I buy a selection of fans just to try them, and put back the surplus in a parts-locker .
Last year, I was planning to build another system from spare parts -- identical in most ways to the one I have, but an improvement. I had to set the work in progress aside, in an initial stage.
So I picked up my project this year. I was stunned that I had actually bought - and installed -- a Delta 5,000 rpm PWM 120mm fan for the exhaust, sitting behind the cooler in ThermalRight's patent accordion duct. Somehow, I'd also picked up a Noctua 120mm iPPC 3000. I swapped the Noctua for the Delta today in the case.
I don't know what possessed me to put that Delta in there. It draws 1.46 Amps, well over the limit that most motherboard fan-ports are spec'd for.
I try to get as much airflow as I can, and direct it. But even with the iPPC fans, my machines are quiet. I'm not so sure the Delta could be tamed to lower decibels.