use strict;
use warnings;
use Benchmark qw/ cmpthese /;

my $R = 'R' x 42_000;
my $Q = 'Q' x 42_000;

sub foo {
    my $c = shift;

    pos $$c = 0;
    while ( 1 ) {
        next if $$c =~ /\G\d+R/;
        last unless $$c =~ /\w/g;
    }
}

cmpthese -3, { 
    R => sub { foo( \$R )},
    Q => sub { foo( \$Q )},
}