Usually that shouldn't matter as much as both have small process sizes compared to OS threads or processes. But at millions of connections it starts to matter. Whatsapp for example, was running on FreeBSD and Erlang with 2M+ connections.
Erlang is an ok language with a great runtime. Elixir is much higher level language and hence more productive for teams that already know Erlang but want to write less code and build faster. Also with Erlang, static type checking not used much in Erlang and big loss unless you use dialyzer. Advantage go for compiling and running test cases laser-blindingly fast. There is a native QuickCheck framework for Erlang, and I'm sure someone wrote a go one.
This is building the tool chain and standard library on my modest machine with a cold cache:
$ time ./make.bash
real 0m42.763s
user 1m11.655s
sys 0m13.411s