use Benchmark 'cmpthese';
my %hash;
cmpthese( 10000000, {
   with => sub {delete $INC{strict.pm}; use strict 'refs'; my $a = 1; my $b = 2},
   without => sub {delete $hash{key}; my $a = 1; my $b = 2},
} );

__DATA__
Benchmark: timing 10000000 iterations of with, without...
      with:  8 wallclock secs ( 9.10 usr +  0.00 sys =  9.10 CPU) @ 1098538.94/s (n=10000000)
   without:  3 wallclock secs ( 4.04 usr +  0.00 sys =  4.04 CPU) @ 2478314.75/s (n=10000000)
             Rate    with without
with    1098539/s      --    -56%
without 2478315/s    126%      --