That's not about how much the code might be optimized. I could always step out of Python and do a C module if I needed speed.
Instead, what's valuable in terms of the perceived performance delta is the speed of standard code as one would write intuitively and conventionally. With a reasonable understanding of how CPython compiles and interprets code, and a reasonable understanding of how the standard Go compiler suite generates binary code, one can make ballpark-style statements of performance for such code without lying too much.
Sure, there's PyPy, and there's gccgo, but that's not what most of the respective communities are using today, and it's not what we use in the projects I'm part of either.
Go has pprof which allows for profiling of your code to help find the hotspots. Without a specific case it's hard to say that Go is fast or slow compared to other languages.