I use a noctua fan. It doesn’t cool any better than the stock fan. It’s just way quieter. The cooler is more important for overclocking.
Discussion
I figured quieter is better. Especially since overclocking .6 TH won’t change much
I’ve noticed the biggest determining factor of stable overclocking is ambient temperature. I can push my bitaxe to almost 2 TH the winter. It’s just a little over 1 TH in the summer.