My advice would be to find out for yourself and don't believe the hype:
> Would you say Go is more suited for high-performance command-line tools, and Elixir for long-term running stuff?
Like Go isn't very high performance. See for yourself: http://benchmarksgame.alioth.debian.org/ (I know, lies, damn lies and benchmarks, but it's the best we got!). Elixir is it good for marathons because it's based on Erlang and Ericsson claims six nines uptime? Just use the tech you find is most FUN to work with because it's better to have fun programming than being bored.
Also it depends on the system you are building. Elixir and Erlang scale great and send messages even between servers fast! So if you need to scale it is great. Go I am sure is faster performance wiz but Elixir/Erlang will stay running longer and be easier to reason about as the system gets bigger. Go will be easier to find devs then Elixir/Erlang will be harder. So there are trade offs.
In the end you could use both, use the right tool for the job.
> Would you say Go is more suited for high-performance command-line tools, and Elixir for long-term running stuff?
Like Go isn't very high performance. See for yourself: http://benchmarksgame.alioth.debian.org/ (I know, lies, damn lies and benchmarks, but it's the best we got!). Elixir is it good for marathons because it's based on Erlang and Ericsson claims six nines uptime? Just use the tech you find is most FUN to work with because it's better to have fun programming than being bored.