I've updated my multi-precision Fibonacci C++ package in Go. I am currently in the process of learning Go and this is something I thought I could tackle. I was surprised at how easy it was to build this. I'm becoming a reluctant convert. The implemntation complexity is comparable to Python and I'd say far easier than C++. The performance is incredible, C-like.
I was able to compute F(50M) in about 30s on my i7 Mac.