snippet.rb

require 'benchmark'

count = 10_000_000
Benchmark.bm(10) do |bm|
  bm.report('control') { count.times { [1,2,3,4,5,6] } }
  bm.report('splat')   { count.times { [1,2,3, *[4,5,6]] } }
  bm.report('plus')    { count.times { [1,2,3] + [4,5,6] } }
  bm.report('flatten') { count.times { [1,2,3, [4,5,6]].flatten } }
end

#                 user     system      total        real
# control     4.550000   0.030000   4.580000 (  4.781043)
# splat       9.100000   0.060000   9.160000 (  9.354983)
# plus       10.130000   0.070000  10.200000 ( 10.392451)
# flatten    31.850000   0.210000  32.060000 ( 32.804879)