Benchmark::cmpthese(5000, {
   'outside' => sub { 
         my $x; my $y; my @z; my $i; 
         for ($i = 0; $i < 1000; $i++) {
            $x = $i;
            $y = $x;
            @z = ($x, $y)
         }
            },
   'inside' => sub {
            for (my $i=0; $i < 1000; $i++) {
               my $x = $i; 
               my $y = $x; 
               my @z = ($x, $y)}
            }
});

         Rate  inside outside
inside  120/s      --    -13%
outside 138/s     15%      --