use Benchmark qw(cmpthese);
cmpthese(10000000, {
  single => sub {$foo = 'http://www.yoursite.com'},
  double => sub {$foo = "http://www.yoursite.com"},
});

##</code><code>##

            Rate double single
double 2865330/s     --    -2%
single 2915452/s     2%     --