Code speed comparison

function versus(callable $first, callable $second, $repeat = 100000) {

  $f = microtime(true);
  foreach (range(0, $repeat) as $r) call_user_func($first);
  $firstTimer = microtime(true) - $f;

  $s = microtime(true);
  foreach (range(0, $repeat) as $r) call_user_func($second);
  $secondTimer = microtime(true) - $s;

  printf(
    '%s function is %.2f%% faster (%f vs %f)',
    $firstTimer < $secondTimer ? 'First' : 'Second',
    abs((($firstTimer - $secondTimer) / $firstTimer) * 100),
    $firstTimer, $secondTimer
  );
}

Example

versus(
  function () {
    $str = '!loremipsum';
    return substr($str, 0, 1) === '!';
  },
  function () {
    $str = '!loremipsum';
    return $str[0] === '!';
  }
);

Will print:

Second function is 36.72% faster (0.142766 vs 0.090349)