I'm not sure why you have the regex engine check if each character is not a newline in isook. Use the "s" modifier!

Interesting about pack. I heard the overhead to start the regex engine went up in 5.10, but it seems rather minor when put into perspective. ...except I can't replicate your results.

use strict;
use warnings;

use Benchmark qw(:all);

print("This is Perl $]\n");

my %tests = (
    repeat => 'my ($y,$m,$d) = $date =~ /(\\d\\d\\d\\d)(\\d\\d)(\\d\\d
+)/;',
    range  => 'my ($y,$m,$d) = $date =~ /(\\d{4})(\\d{2})(\\d{2})/;',
    isook  => 'my ($y,$m,$d) = $date =~ /(....)(..)(..)/s;',
    unpack => 'my ($y,$m,$d) = unpack "A4 A2 A2", $date;',
);

# These don't result in any opcodes.
$_ = 'use strict; use warnings; our $date; '.$_
    for values(%tests);

our $date = '20091202';

my $results = cmpthese(-3, \%tests);
[download]

This is Perl 5.010000
           Rate  range repeat  isook unpack
range  405773/s     --    -6%    -8%   -46%
repeat 432956/s     7%     --    -2%   -43%
isook  441233/s     9%     2%     --   -42%
unpack 757010/s    87%    75%    72%     --

This is Perl 5.010000
           Rate  range  isook repeat unpack
range  398141/s     --    -7%    -7%   -47%
isook  427913/s     7%     --    -0%   -43%
repeat 429311/s     8%     0%     --   -43%
unpack 751802/s    89%    76%    75%     --

This is Perl 5.010000
           Rate  range repeat  isook unpack
range  415595/s     --    -7%    -8%   -45%
repeat 445365/s     7%     --    -1%   -41%
isook  449974/s     8%     1%     --   -40%
unpack 754290/s    81%    69%    68%     --
[download]

The faster way seems to be using the capture made of dots as in "isook"

You haven't shown that. Any difference less than 5% should be ignored. It's within the error margin.