文字連結の処理速度

// 追記編
$time1 = getmicrotime();
$str = null;
for($n = 0; $n < $count; $n++){
    $str.= $str1;
    $str.= $str2;
    $str.= $str3;
}
$time1 = getmicrotime() - $time1;
 
// 連結編
$time2 = getmicrotime();
$str = null;
for($n = 0; $n < $count; $n++){
    $str.= $str1.$str2.$str3;
}
$time2 = getmicrotime() - $time2;
 
// 非連結編
$time3 = getmicrotime();
$str = null;
for($n = 0; $n < $count; $n++){
    $str.= "$str1$str2$str3";
}
$time3 = getmicrotime() - $time3;
 
// 配列編1
$time4 = getmicrotime();
$arr = array();
for($n = 0; $n < $count; $n++){
  array_push($arr, $str1, $str2, $str3);
}
$str = implode('', $arr);
$time4 = getmicrotime() - $time4;
 
// 配列編2
$time5 = getmicrotime();
$arr = array();
for($n = 0; $n < $count; $n++){
  $arr[] = $str1;
  $arr[] = $str2;
  $arr[] = $str3;
}
$str = implode('', $arr);
$time5 = getmicrotime() - $time5;