I agree 100% to the C-Solutions :). "split" is only reliable if the `key' cannot have spaces, CSV then might be a lot easier (and more portable)

I also don't think 300 is a *big* config file.

use strict;
use warnings;

use Benchmark qw(timethese cmpthese);
use YAML qw();
use YAML::Syck qw();
use XML::Simple qw();
use Config::Fast qw();
use Text::CSV_XS;

my $x = "x" x 100;
my %bigHash = map { $_ => "Str ".substr $x, int rand 100 } map { "x$_"
+ } 0..3000;

YAML::DumpFile ("delme.yml", \%bigHash);

open my $out, ">", "delme.xml" or die "Can't create demle.xml: $!\n";
print $out XML::Simple::XMLout (\%bigHash);
close $out;

open $out, ">", "delme.fst" or die "Can't create delme.fst: $!\n";
print $out "$_ $bigHash{$_}\n" for keys %bigHash;
close $out;

my $csv = Text::CSV_XS->new ({ binary => 1, eol => "\n" });
open $out, ">", "delme.csv" or die "Can't create delme.csv: $!\n";
$csv->print ($out, [ $_, $bigHash{$_} ]) for keys %bigHash;
close $out;

cmpthese (
    -3, {
    YAML => sub { my $newHash = YAML::LoadFile           ("delme.yml")
+; },
    Syck => sub { my $newHash = YAML::Syck::LoadFile     ("delme.yml")
+; },
    fast => sub { my $newHash = Config::Fast::fastconfig ("delme.fst")
+; },
    XML  => sub { my $newHash = XML::Simple::XMLin       ("delme.xml")
+; },
    slurp => sub {
        local @ARGV = "delme.fst";
        my %newHash = map { split " ", $_, 2 } <>;
        },
    csv   => sub {
        open my $fh, "<", "delme.csv";
        my %newHash;
        while (my $row = $csv->getline ($fh)) {
        $newHash{$row->[0]} = $row->[1];
        }
        },
    });
[download]

=>

        Rate  YAML   XML  fast   csv  Syck slurp
YAML  1.39/s    --  -10%  -54%  -97%  -98%  -99%
XML   1.54/s   11%    --  -49%  -97%  -98%  -99%
fast  3.02/s  117%   96%    --  -94%  -96%  -98%
csv   47.2/s 3289% 2959% 1462%    --  -43%  -65%
Syck  82.2/s 5804% 5228% 2622%   74%    --  -39%
slurp  136/s 9638% 8689% 4389%  187%   65%    --
[download]