use strict;
use warnings;
use feature 'say';
use Time::HiRes 'time';

say $^V;

my $s = '*' x 5_000_000;
$s .= "0123456789 01234 n \n" x 40_000;

my $re = qr/ (\d{10}) \x{20} (\d{5}) \x{20} (\w) \s\s /x;
my ( $xref, $t );

                                # (1) peel off entry by entry
$xref = substr $s, 5_000_000;   # from shorter string
$t = time;
for ( 0 .. 39_999 ) {
    my $entry = substr $xref, $_ * 20, 20;
    die unless $entry =~ / \A $re /x;
    
    # do something useful with captures
    
}
say time - $t;

$xref = substr $s, 5_000_000;   # (2) global match (shorter string)
$t = time;
for ( 0 .. 39_999 ) {
    die unless $xref =~ / \G $re /gx;
}
say time - $t;

                                # (3) global match (original string),
pos( $s ) = 5_000_000;          # start from pos
$t = time;
for ( 0 .. 39_999 ) {
    die unless $s =~ / \G $re /gx;
}
say time - $t;

$xref = \substr $s, 5_000_000;  # (4) use reference to substr
$t = time;
for ( 0 .. 39_999 ) {
    die unless $$xref =~ / \G $re /gx;
}
say time - $t;


__END__

v5.40.0
0.0973920822143555
0.04703688621521
0.0475959777832031
3.08383107185364