No mechanical apparatus with moving parts is silent. You'd have to have a really big fan not to hear it at all in the case unless you have poor hearing. The only way to be silent is not to have a fan. It is actually possible with a well designed case and airflow system to not have more than a single fan or any fan at all even in a higher end system. It's a matter of thermodynamics. Unless you've done the math, (and unless you're a electrical or mechanical engineer, i seriously doubt you have the skill set) about how that particular heat sink works, you really don't know what you're talking about.
"Any decent to good fan (Phanteks or Noctua for example) attached to a large tower can be pretty much silent, especially in a case geared toward being quiet. 140mm fans are 'almost' silent around the 500-600rpm range while allowing the heatsink to me that much more effective. Just like a huge watercooling radiator with fans running at a very low rpm. Some air flow is better than none.
I guess a low powered cpu (i3 or pentium) would work well with this but who puts those weak chips in large enclosures? I like the idea of an i3 or Pentium in a tiny itx box or a box that the user does not care about sound. "