gistfile1.txt

$ ./bench_array_join.rb 
                user     system      total        real
a[a.length, 0]  0.010000   0.000000   0.010000 (  0.012573)
a += b      3.240000  10.560000  13.800000 ( 50.623165)
a.push *b   0.010000   0.000000   0.010000 (  0.026780)


$ cat bench_array_join.rb 
#!/usr/bin/ruby

require 'rubygems'
require 'benchmark'

n = 20_000

b = 8,9,10,11,12,13

Benchmark.bm(10) do |x|
  x.report("a[a.length, 0]") { a = 1,2,3,4,5,6,7; n.times do; a[a.length, 0] = b; end }
  x.report("a += b")   { a = 1,2,3,4,5,6,7; n.times do; a += b; end }
  x.report("a.push *b"){ a = 1,2,3,4,5,6,7; n.times do; a.push *b; end }
end