for( 30, 300, 3000, 30000 ) { 
    $s = 'x'x$_ . 'reg exp' . 'x'x$_; 
    study $s; 
    cmpthese -1, { 
        REGEX => q[ $x = $s =~ /reg exp/;], 
        INDEX => q[$x = index $s, 'reg exp';] 
    } 
};;
           Rate REGEX INDEX
REGEX 2101154/s    --  -28%
INDEX 2912801/s   39%    --

           Rate REGEX INDEX
REGEX  829929/s    --  -32%
INDEX 1224656/s   48%    --

          Rate REGEX INDEX
REGEX 100781/s    --  -38%
INDEX 161881/s   61%    --

         Rate REGEX INDEX
REGEX 10983/s    --  -26%
INDEX 14792/s   35%    --