Unqualified "fast enough" is pretty much exactly the problem being pointed out. Most developers have no idea what "fast" is let alone "fast enough". If they were taught to benchmark at with a lower level language, see what adding different abstractions causes, that would help a ton.
I would personally suggest C++ though because there is such a huge amount of knowledge around performance and abstraction in that community - wonderful conference talks and blog posts to learn from.
Go comes from a different school of compiler design where the code generation is decent in most cases, but struggles with calculations and more specific patterns. Delphi is a similar compiler. Looking at benchmarks, the performance is only a few times worse than optimized C. That's on par with the most optimized JITed languages like Java, while being overall a much simpler compiler. I feel it is is fair to say 'good enough' in this situation.
It's not an "unqualified" claim, Go really is fast enough compared to the likes of Python and Ruby. I'm not saying that rewriting a Go program in a faster language (C/C++/Rust) can't sometimes be effective, but that's due to special circumstances - it's not something that generalizes to any and all programs.
I would personally suggest C++ though because there is such a huge amount of knowledge around performance and abstraction in that community - wonderful conference talks and blog posts to learn from.