# for (1..$elements) {
#    my ($key, $one, $two) = rand =~/(\d\.\d{2})(\d{2})(\d{4})/;
#   $hash{$key} = [$one, $two];
#}

for (1..$elements) {
    my ($one, $two) = rand =~/\d+.(\d{6})(\d{4})/;
    $hash{$_} = [$one, $two];
}

# Also reduced $elements to 200_000 and 2 million 
# exceeded per proc memeory limit.

# I also use more entropy in the field to sort on 
# requiring a change of packed_default to ...

sub packed_default {
    my @sorted_keys =
        map substr($_,4),
        sort map {pack('N', $hash{$_}[0])."$_"}
        keys %hash;
    return @sorted_keys;
}

Benchmark: timing 10 iterations of BroweserUK, packed_default...
BroweserUK: 188 wallclock secs 
    (175.63 usr +  0.13 sys = 175.76 CPU) @  0.06/s (n=10)
packed_default: 72 wallclock secs 
    (64.61 usr +  0.16 sys = 64.77 CPU) @  0.15/s (n=10)