Since it feels like there's some disagreement about what the maximum attack speed actually is, I did an experiment ages ago (over a year) to find out. With the recent updates there has been some questions about whether or not that has changed, so I repeated my tests and found that no, it hasn't changed.

By using different combinations of kit, I had each attack speed from 0 to 22, and for each one I hit the trainer for exactly 1 minute and counted how many hits in the chat window.

Note that due to rounding / timing issues each of the results could be out by as much as 2 hits either way, which accounts for why sometimes faster speeds appear to have 1 less hit than a slower speed, and sometimes the increase doesn't seem very linear, that's not likely to be the case, it'll just be that one or both of those results will be out by 1 or 2 hits.

Here are the results

Attack Speed |
Hits in 1 minute |

0 |
55 |

1 |
54 |

2 |
58 |

3 |
60 |

4 |
61 |

5 |
63 |

6 |
65 |

7 |
68 |

8 |
71 |

9 |
72 |

10 |
76 |

11 |
77 |

12 |
80 |

13 |
83 |

14 |
88 |

15 |
91 |

16 |
95 |

17 |
97 |

18 |
98 |

19 |
97 |

20 |
97 |

21 |
97 |

22 |
97 |