I'm pretty sure those should turn out to be almost exactly the same. If speed is that important, perhaps you should look at assembly language or C or something? You can always import those routines into perl later using XS.

You could check using Benchmark:

use strict;
use Benchmark;

my %h = (hrmph => 1);
my $h = \%h;

timethese( 10_000_000, {
  lhs => sub { $h{hrmph} },
  rhs => sub { $h->{hrmph} },
});
[download]

Curiously, $h{hrmph} seems to actually be measurably faster, but by a very tiny amount.