When I run tobyink's benchmark under 5.18, I get a 20% reduction in runtime:

C:\test>\perl5.18\bin\perl.exe
use strict;
use warnings;
use Benchmark qw(cmpthese);

my $name = 'foo';
my $path = 'foobar';
my $sub1 = sub { $_[0]{$path}{$name} = $_[1] if @_ == 2; $_[0]{$path}{
+$name} };
my $sub2 = eval qq[ sub { \$_[0]{$path}{$name} = \$_[1] if \@_ == 2; \
+$_[0]{$path}{$name} } ]
        or die($@);

my $self = {};

cmpthese -1, {
        closure => sub {
                $self->$sub1(0);
                $self->$sub1( $self->$sub1 + $_ ) for 0..10_000;
        },
        stringy => sub {
                $self->$sub2(0);
                $self->$sub2( $self->$sub2 + $_ ) for 0..10_000;
        },
};
^Z
          Rate closure stringy
closure 65.7/s      --    -17%
stringy 79.1/s     20%      --
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If you got a 20% rise, you'd consider it "significant".

If you were offered a 20% reduction in the cost of your next car, you'd consider it "significant".

If you were offered a 20% reduction in your likelihood of early mortality, you'd consider it "significant".

If you were gifted a 20% reduction in your daily processing, such that it reduced it from 25 hours to 20, you'd consider it "significant".

Stop being an ass.