$concat = 999999 x 'abcdefghijklmnopqrstuvwxyz'; 

##</code><code>##

use Benchmark 'cmpthese';
use strict;
use warnings;

my @stuff = 1 .. 20000;

cmpthese(-3, {
    'for EXPR' => sub {
        my $a = 0;
        ++$a for @stuff;
    },
    'for BLOCK' => sub {
        my $a = 0;
        for (@stuff) { ++$a }
    },
    'map BLOCK' => sub {
        my $a = 0;
        map { ++$a  } @stuff;
    },
    'map EXPR' => sub {
        my $a = 0;
        map ++$a, @stuff;
    },
});
__END__
            Rate map BLOCK  map EXPR for BLOCK  for EXPR
map BLOCK 50.4/s        --       -4%      -44%      -49%
map EXPR  52.3/s        4%        --      -42%      -47%
for BLOCK 89.9/s       78%       72%        --       -9%
for EXPR  98.6/s       96%       89%       10%        --

This is perl, v5.8.0 built for MSWin32-x86-multi-thread