Rate    WithCopy WithoutCopy
WithCopy    450450/s          --         -9%
WithoutCopy 495050/s         10%          --
[download]

use strict;
use Benchmark qw(:all);
 
my %data = (
    Lore    =>'mipsumdo', ente    =>'squemoll',
    lors    =>'itametco', isod    =>'ioetnonu',
    nsec    =>'tetuerad', mmyf    =>'acilisis',
    ipis    =>'cingelit', augu    =>'eliberoi',
    Sedr    =>'honcusma', acul    =>'isodioat',
    ssai    =>'dmollisp', cons    =>'ectetuer',
    hare    =>'travelit', nisl    =>'nislquis',
    null    =>'amattise', feli    =>'sDonecma',
    nimq    =>'uisferme', gnar    =>'isusulla',
    ntum    =>'nequenul', mcor    =>'peridele',
    lase    =>'dduiDone', ifen    =>'dutfeugi',
    cbla    =>'nditmetu', atas    =>'emAliqua',
    svit    =>'aecondim', msed    =>'magnaado',
    entu    =>'mluctusa', lorn    =>'onummysa',
    ntem    =>'assaeuis', gitt    =>'isNuncne',
    moda    =>'nteaport', corc    =>'iMorbima',
    amii    =>'psumnonl', ttis    =>'blandits',
    eoAl    =>'iquamcon', emPh    =>'asellusq',
    dime    =>'ntumblan', uiso    =>'rciInfer',
    ditf    =>'elisPell', ment    =>'umturpis',
);
 
sub WithCopy {
    my $hashref = $_[0];
 
    my @dummy1 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy2 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy3 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy4 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy5 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy6 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy7 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy8 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy9 = @{$hashref}{'Lore','lors','nsec'};
    my @dummy0 = @{$hashref}{'Lore','lors','nsec'};
}
 
 
sub WithoutCopy {
   my @dummy1 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy2 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy3 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy4 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy5 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy6 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy7 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy8 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy9 = @{$_[0]}{'Lore','lors','nsec'};
   my @dummy0 = @{$_[0]}{'Lore','lors','nsec'};
}
 
 
cmpthese(500000, {
    'WithCopy'        => 'WithCopy(\%data);',
    'WithoutCopy'    => 'WithoutCopy(\%data);',
});
 
__END__
               Rate WithoutCopy    WithCopy
WithoutCopy 82645/s          --         -8%
WithCopy    89445/s          8%          --
[download]

Which seems to show that the performance increase is less when you index the @_ array a lot.

Of course it doesn't show that - it could also mean that the time needed to copy the keys of the hash reference 10 times overshadows the time needed to index the array and/or copy the hash reference, thereby decreasing the influence of doing either.

Benchmarking is hard.