use Benchmark 'cmpthese';

my %hash = ( key => 'value' );

cmpthese( -10, {
   with =>	q[
	   BEGIN{ delete $INC{'strict.pm'}; use strict 'refs' }
	   my $a = 1; my $b = 2
	],
   without => q[
	   BEGIN{ $hash{'key'} = delete $hash{key} }
	   my $a = 1; my $b = 2
	],
} );

__END__
P:\test>..\bin\perl.exe junk.pl8
            Rate    with without
with    368780/s      --     -2%
without 375558/s      2%      --

P:\test>..\bin\perl.exe junk.pl8
            Rate    with without
with    371638/s      --     -1%
without 374367/s      1%      --