I'm also interested in Noiseblocker BlackSilent PK1, they seem excellent as well. Anyway, all input is extremely appreciated!
While the PK1 is an excelent fan tonally, it has its drawbacks, like you cant undervolt it, or doesnt have much effect, at least on mine.
While the Antec True Quiet 140s, have a very good range of operation, depending on the motherboard it can be drop off to 200rpms and scale up to 800rpms,
Sadly i dont own any of the Noctua Redux, the 140s seems more using the design of the P14 that SPCR had as their reference fan, not like the newer A14, but in my experience Noctua has very good range of operation, specially for PWM fans and their coolor scheme of the redux seems attractive for most, so if thats important to you, then i think its a good option, just a matter of deciding into if you want PWM or 3pin voltage controlled.