my $c;
for ( my $i = 0; $i < length($string); $i++ ) { 
    $c = substr( $string, $i, 1);
}

##</code><code>##

$string is 3000 bytes
Benchmark: running for, split, each for at least 10 CPU seconds...
       for: 10 wallclock secs (10.31 usr +  0.00 sys = 10.31 CPU) @ 123.73/s (n=1275)
     split: 10 wallclock secs (10.58 usr +  0.00 sys = 10.58 CPU) @ 117.15/s (n=1240)

+5%

$string is 10000 bytes
Benchmark: running for, split, each for at least 10 CPU seconds...
       for: 11 wallclock secs (10.33 usr +  0.00 sys = 10.33 CPU) @ 36.96/s (n=382)
     split: 11 wallclock secs (10.44 usr +  0.00 sys = 10.44 CPU) @ 34.08/s (n=356)

+8%

$string is 30000 bytes
Benchmark: running for, split, each for at least 10 CPU seconds...
       for: 10 wallclock secs (10.19 usr +  0.00 sys = 10.19 CPU) @ 12.36/s (n=126)
     split: 10 wallclock secs (10.60 usr +  0.00 sys = 10.60 CPU) @ 10.57/s (n=112)
     
+16%     


##</code><code>##

use Benchmark;
my $string = "1234567890" x 5000 ;

print "\$string is " . length( $string ) . " bytes \n";

timethese(-10,{split=>sub{  
					for my $c (split //, $string) {  }   
                      },
             for=>sub{ 
             
					my $c;
					for ( my $i = 0; $i < length($string); $i++ ) { 
						$c = substr( $string, $i, 1);
					}
             
              }});