append_bench.exs

defmodule AppendBench do
  use Benchfella
  
  @list Enum.into 1..10000, []

  bench "++" do
    h = Enum.at @list, 0
    @list ++ [h]
  end

  bench "List.insert_at" do
    h = Enum.at @list, 0
    List.insert_at @list, -1, h
  end
end

Settings:
duration: 1.0 s

AppendBench

[19:01:09] 1/2: List.insert_at
[19:01:12] 2/2: ++

Finished in 7.31 seconds

AppendBench

++ 50000 64.73 µs/op
List.insert_at 10000 298.41 µs/op