> The two fastest brokers I have found are emqtt and Mosquitto
What about vernemq? I [ran across][1] a comment a while back about some tradeoffs with emqtt's usage of mnesia. Haven't gotten around to trying verne myself yet though.
We can have a big bench-off with more brokers later on. I have tested maybe 6 and from this I have decided to write my own. I wouldn't spend time reinventing the wheel for free if I didn't have a reason for it :) Then you also have memory usage which is impossible to optimize in VM/GC languages.