I'm surprised that the discussion about replacement fans are more focused on their airflow volume (CFM) rather than static pressure (mm/H2O) which is more significant in heat sink/radiator applications. High static pressure fans are more capable of penetrating through dense heat sink fins such as in the AntMiner devices. I think there's a reason why Bitmain engineers equip their units with very powerful industrial 12038s with high static pressure (directly proportional to loudness) instead of just mainstream consumer-oriented 12025s.
true in the case of one push fan only. but two high cfm fans as push pull get around that.
since neither one needs full penetration of the heat sink using high static pressure, but if you don't care about sound the stock fan with a good pull fan cools best.
Push-pull configuration is only effective in an enclosed unit (S3) and not in an open-chassis design (S5) though.