Golang certainly is quite efficient, probably close to C or C++. It also has lightweight threads which are great and terrible at the same time: you can take the thread-based concurrency model further without resource problems. And the CSP approach helps to make that somewhat safe. But at the end of the day any concurrency built on threads, even lightweight ones, is problematic.
It is a ridiculously low-level in terms of abstractions language though, just a tiny notch above C. Perl 6 is quite on the opposite end of that scale.
For me the most important differences are cultural however: Perl 6 is quite open and inclusive, both people and the language it self. TIMTOWTDI. I don't think I can or want to describe the Golang culture, but it certainly is quite different.
The good thing about Golang is that as a language it is so simple/primitive that you can easily try it out for yourself and get a comprehensive picture over a weekend.