array_benchmark.rb

#!/usr/bin/env ruby

require 'benchmark'

Benchmark.bmbm do |x|
  x.report("Push x2") do
    ary = []
    100000.times do
      ary << 'hi'
      ary << 'hihi'
    end
  end

  x.report("Concat ary") do
    ary = []
    100000.times do
      ary += ['hi', 'hihi']
    end
  end
end

output.txt

# Ruby 2.1.2
$ ruby ./array_benchmarks.rb 
Rehearsal ----------------------------------------------
Push x2      0.030000   0.010000   0.040000 (  0.040183)
Concat ary  20.480000  19.230000  39.710000 ( 39.916032)
------------------------------------ total: 39.750000sec

                 user     system      total        real
Push x2      0.030000   0.000000   0.030000 (  0.026020)
Concat ary  19.810000  18.560000  38.370000 ( 38.427382)