Of course, where this really matters is doing something not doing nothing and there, of course, the delta is less significant. (Though still greater than zero.)

package Foo;

sub do_something { my $i; $i++ for (1 .. 10) }

package main;
use strict;
use warnings;

use Benchmark qw( cmpthese );

my $foo = bless {}, 'Foo';

sub do_something { my $i; $i++ for (1 .. 10) }

cmpthese( -1, {
    k1 => sub { $foo->do_something },
    k2 => sub { Foo->do_something  },
    k3 => sub { Foo::do_something  },
    k4 => sub { do_something       },      
    k5 => sub { &do_something      },      
});
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       Rate  k2  k1  k4  k3  k5
k2 359975/s  -- -3% -6% -7% -8%
k1 369628/s  3%  -- -3% -5% -6%
k4 382293/s  6%  3%  -- -2% -3%
k3 388120/s  8%  5%  2%  -- -1%
k5 392991/s  9%  6%  3%  1%  --
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