Stock fan produces ~69db, which is not typically tolerable in the house (apart from basement, attic, garage, shed)
Fan play to have as much hash as possible while maintaing low dB:
~30C ambient
1. Noctua 3000 PWM ($24.5, 110CFM, up to 3000rpm, just 41dB) in push position: ~59-61C at 325mhz, 1070Gh; less stable at 350mhz.
2. Scythe Ultra KAZE ($15.3, 130CFM, 3000rpm, 46dB) in push position via molex adapter-worse than Noctua, temp rising close to 65C at 325mhz, discontinued. Strange result as this fan has nominally higher CFM than Noctua.
3. Noctua in push, Scythe in pull (connected to molex through included adapter), up to 337.5 mhz is stable (1100 Gh).

Conclusion: adding Scythe ($15) in pull might be not worth it as it adds just ~30gh.
I simply taped Scythe to exhaust in pull orientation because could not find proper screws yet.

Question: anybody knows what are the characteristics/dimensions of the machine screws Bitmain is using for fans? They seem to be in between 3 and 4mmX42mm, but I wasn't able to find such screws easily. They are not 3X40mm for sure. Anybody have a link?