I replaced all my fans with Scythe Kaze minis. One fan failed (got very noisy) because i blew air on the board with a 92mm fan, diagonal from above. Not very clever i know ! That destroyed the bearing in less than 2 months The minis are a bit quieter but they don't deliver the same airflow as the stock fans. Scythe is 14 dB/A, 4,11 CFM, Xilence (stock) 19 db/A, 5,28 CFM.
The stock fans are a good balance between noise and effective cooling for a stand-alone board. Since i use additional fans to cool my units and the noise was too loud, i went with the minis. Very happy so far.