Benchmarking to_s vs. &&=. Result: &&= is faster

bench.rb

require 'benchmark/ips'                                                                                                                       

ENV = {}                                                                                                                                      
Benchmark.ips do |x|                                                                                                                          

  x.report("to_s, then to_s", "content_type = ENV['CONTENT_TYPE'].to_s.split(/\s*[;,]\s*/, 2).first.to_s.downcase")                           
  x.report("to_s, then &&=", "content_type = ENV['CONTENT_TYPE'].to_s.split(/\s*[;,]\s*/, 2).first; content_type &&= content_type.downcase")
  x.report("&&=, then &&=", "content_type = ENV['CONTENT_TYPE']; content_type &&= content_type.split(/\s*[;,]\s*/, 2).first; content_type &&= content_type.downcase")  
  
end

result.txt

2014 MacbookPro Mavericks, rvm
ruby-1.9.3-p545

Calculating -------------------------------------
     to_s, then to_s     70050 i/100ms
      to_s, then &&=     77667 i/100ms
       &&=, then &&=    143708 i/100ms
-------------------------------------------------
     to_s, then to_s  1269626.8 (±6.0%) i/s -    6374550 in   5.041295s
      to_s, then &&=  1740026.1 (±6.0%) i/s -    8698704 in   5.020302s
       &&=, then &&=  8527095.9 (±6.8%) i/s -   42393860 in   5.000842s
       
ruby-2.0.0-p451

Calculating -------------------------------------
     to_s, then to_s     81304 i/100ms
      to_s, then &&=     91575 i/100ms
       &&=, then &&=    154433 i/100ms
-------------------------------------------------
     to_s, then to_s  1455078.0 (±4.7%) i/s -    7317360 in   5.040880s
      to_s, then &&=  1888529.5 (±6.0%) i/s -    9432225 in   5.015203s
       &&=, then &&=  9195450.3 (±7.9%) i/s -   45557735 in   5.000975s
       
jruby-1.7.11

Calculating -------------------------------------
     to_s, then to_s    147789 i/100ms
      to_s, then &&=    188934 i/100ms
       &&=, then &&=    300286 i/100ms
-------------------------------------------------
     to_s, then to_s  3927350.8 (±5.2%) i/s -   19655937 in   5.022000s
      to_s, then &&=  4511127.9 (±4.1%) i/s -   22672080 in   5.035000s
       &&=, then &&= 14960140.8 (±6.3%) i/s -   74470928 in   5.003000s
       
rbx-2.2.6

Calculating -------------------------------------
     to_s, then to_s    191145 i/100ms
      to_s, then &&=    278214 i/100ms
       &&=, then &&=    410259 i/100ms
-------------------------------------------------
     to_s, then to_s  4369199.9 (±5.7%) i/s -   21790530 in   5.009839s
      to_s, then &&=  6058620.2 (±4.4%) i/s -   30325326 in   5.017248s
       &&=, then &&= 15879119.6 (±6.1%) i/s -   79179987 in   5.011392s