Scythe Fans are generally very good and quiet, my Scythe Ninja Plus came with a 120mm fan (scythe of course) which runs at full speed and I don't hear it. I sit right next to my PC mid-town (on the floor) and overall my PC is very quiet.
I don't have any but I would be extra careful to keep all wires and fingers away while they are on. I know this sounds like a no brainer but it happens. Anyway, I heard that it doesn't take a lot of extra tension on the blades to cause the motor to throw oil all over the inside of you case.
According to one of Germany's more respected hardware magazines, the Scythe S-Flex SFF21E is the best (Note the "E" at the end), followed by the new Noctua NF-S12-1200 and then a Yate Loon (forget the model number). The Aerocool Turbine 1000 came fourth I think.
The SilenX is apparently really bad at what it does and the testers couldn't find any reason behind the price tag. Perhaps "really bad" is the wrong phrase, but not good enough in any way.
Of course there's a valid argument of against getting a 133cfm fan, since more often than not I won't be using full speed. But seeing that the price is a bout the same and all, just in case my cpu starts overheating or global warming hits us hard, I have the potential to increase my fan speed.
Also, higher speed models are usually better at undervolting.
Just a note to whoever will be reading this thread. I have ordered few of the 133.6cfm fans. http://www.newegg.com/Product/Product.aspx?Item=N82E168.... Performance wise the fan is great, really loud at full speed. So I decided to get a controller HOWEVER if voltage and current drops (from fan controller) the fan will be giving an irritating humming noise. It's very annoying, my advise to you is think twice before you order them.