Speed and maintainability vs trying to optimize high-level FP-esque idioms into fast machine code is a false dichotomy. OCaml has a really fast compiler, it has been maintained by a small team for 25 years, and it produces fast machine code. A big caveat in comparing OCaml and Go would be multicore support, but it's coming in OCaml, without breaking existing programs and with only a few percent of performance lost.