When listening to these fans (all 7 blades, 120mm x 25mm) I listened for the motor noise and ignored the whoosh. From what I've read in SPCR, some of you agree that at the same RPM, the "whoosh" is the same - and some of you don't. So be it; you know how I tested.
Got a couple of new fans in today - an 800RPM (nominal) Evercool 120mm and a YL D12SL-12 (all black). Old fans included S-Flex D and E, the GW NCB, and the Ninja Plus fans.
This was my first attempt at comparing fans as slow as 860RPM. I quickly discovered that since the fans were quieter at that speed, the differences were smaller, too.
The Ninja-Plus fan is the Scythe model 62027, AD1212DS-A73GL(6TCL3). At 1028RPM, it is exactly as loud and sounds exactly the same as the Scythe S-Flex E. The E sells for $13-$15; Jab-Tech will pay you $4 to carry the 62027 away (the Ninja-Plus is $4 cheaper than the Ninja).
At 1028RPM, the YL12SL-12 is a tad quieter than the GW NCB, which was until now the quietest 120mm fan I'd tested at that speed. When I dropped the RPMs to 860, the advantage of the YL improved some (but the absolute difference dropped - 860RPM noise levels are very low). This YL is my new low-noise champ.
A confession: a year ago, I bought two ~1300RPM all-orange YLs from TekGems. They were both junk, and I threw them away. Thus, my YL aversion. I paid $6 for this YL at SVC, the same price as the GW NCB.
The difference is not enough to make me junk my NCBs, and the NCBs still have those ceramic bearings that're rated for long life. Good for my modded PSUs, which (all 3) have NCBs.
With the arrival of the Evercool, I now have two fans whose nominal speed is 800RPM - the other is an S-Flex D. With the Sunbeam Rheostat 4-channel controller turned up to max, I get 11.41V and 860RPM from each fan (a coincidence, fans vary in speed). These two fans had the same noise level. The Evercool had a slightly higher pitch. I was listening at 3", swapping ears on each comparison to make sure I wasn't holding closer on the right ear or had a better left ear, something like that.
But as an exhaust fan, in the back of a computer case a meter away from you and not in "line of sight"? You'd never hear anything, much less any difference. I could barely hear the fans a foot away! And yes, the YL and NCB (when turned down with the controller) are quieter, but again, a meter away? Forget it!
About the 860RPM: remember I'm at 4100 feet here in Klamath Falls, with 86.4% of sea level air pressure. Fans spin faster. Louder? No, the air is thinner.
The advantage of an 800RPM fan is, if that's the speed you want, you don't have to buy a fan controller. The YL or NCB is better, but you gotta have that controller, and be smart enough not to get suckered into buying a PWM controller. Hint: I use the dual Spire PCI-mount controller. I like being able to turn up the fan speed on really hot summer days.
Fans are getting better. There's some good, cheap fans to choose from these days.