As far as recommending the Noctuas, go to SPCR's forums and read what is being written about them.......true, most, and I stress MOST, of the Noctuas people receive are very quiet, more and more people are beginning to complain of whining noises eminating from their Noctua fans...both the 800 and 1200 rpm fans. Also, don't put ANY restrictions in the path of a Noctua fan.....do that and its air output falls worse than a brick thrown in a pond. The general consensus is use a Noctua for exhaust only.....cannot handle intake duties (too much resistance/restriction for it to pull effectively from the outside of a case through what is normally a convoluted and restricted path to the intake on most cases). And they will tell you to never use a Noctua fan on a heatsink......asking for death.
The hype of Noctua fans is beginning to show up as just that.......and is rapidly falling out of favor on SPCR's forums for anything other than an exhaust fan. But, for $20, your money can be better spent....like a Nexus if you have to have black and white or the aforementioned Yate Loons, if black can do.
As far as SilenX fans.......horrible joke amongst users of quiet fans. Their dB rating is bogus, to say the least. Quite a bit louder than any dB rating they claim to have "measured". Look how they arrive at their dB ratings on their fans. They measure at 1M, 3 ft., from the fan on 3 axes and then calculate a mean of the three measurements to determine their dB rating. Well, shoot, measuring a yard away from the fan and almost anything will sound quiet, especially when you have two measurements that are off-center from the loudest part of the fan.....the front. Taking a mean between a front and two side measurements at a yard away.........bogus measurements and totally useless information. Add in flimsy frames that buzz, too small motors and housings that cause the motors to run very hot, and you've got an overpriced hunk of junk.
Of course, don't mention SilenX fans at SPCR......the owner of the company did a little viral marketing of his own over there.......made several accounts under many different names (at least 4 I know of) on SPCR's forum and posed as an average consumers that thought SilenX products were the sh!t........and pushed them whenever anyone asked an opinion about quiet products. Eventually he was found out.......and disgraced......as their products should be.