Ok aside sh*ting on Bitmain which I understand. I played around with some compressed PVC panels and results are pretty good. Fan on front is Delta TFC1212 5500 rpm.
And with this setup it does not matter if internet connection is lost or pool is not working there is no chance to burn anything...
Easier to just remove the PWM line on the stock fan (I prefer to pull the connector out of the plug then electrical tape it, some folks might prefer to just cut it as that's easier), then it runs at 100% all the time for best cooling.