How Go is compiled isn't as relevant to its performance as much as what Go is compiled into, which hasn't changed all that much as far as I know. The GC improvements might help with latency though.
What are you talking about? Go code generation is getting better all the time.
That said, I took the original statement about Go switching from Co to Go to indicate there's been major changes in the compiler, so it would be interesting to see more recent results, not that the change itself necessarily was responsible for major speed improvements, but they could very well have assumed the compiler change would have had a larger affect on the resulting binary depending on their understanding of the Go toolchain.
> Mosquitto was compiled with gcc 4.8.2, the Go implementation was executed with go run, the D implementation was compiled with dmd 2.0.64.2 and the Erlang version I’m not sure.
The "I'm not sure" speaks for itself, but go run also includes both compilation time and execution time and they're comparing it against just the execution times of the other languages. That's not exactly an apples to apples comparison.
I don't know why you think that start-up time has an effect on the benchmarks. It doesn't matter how long the brokers take to start, once they did the measurements were done. `go run` doesn't change a thing.