...
use Sort::Key qw(ikeysort);
sub SortKey {
    my @sorted_keys = ikeysort { $hash{$_}[0] } keys %hash;
}

cmpthese(10, { BrowserUK => \&BrowserUK,
	       packed_default => \&packed_default,
	       SortKey => \&SortKey });
__end__

                 Rate      BrowserUK packed_default        SortKey

BrowserUK      50.0/s             --           -30%           -45%
packed_default 71.4/s            43%             --           -21%
SortKey        90.9/s            82%            27%             --