> There is a limit to optimization, and that ends with optimized machine code.

There might be a low limit, but there’s no high limit: you can generate completely unoptimised machine code, and that’s much closer to what Go’s compiler does.

> Go being a compiled language, that is cross paltform but separate binaries, should be very close to C in terms of performance.

That’s assuming that Go’s optimisation pipeline is anywhere near what mainstream C compilers provide. Against all evidence.