Split String into 2 strings with lower and upper case. Eg: split("HelloWorld") returns ["HW", "elloorld"]

SplitString.scala

/**
 * `benchmark` function took:
 * scala -nc SplitString.scala  14.71s user 0.50s system 274% cpu 5.532 total
 * on MacbookPro Late 2012 (Core i5 2.5, DDR3 8GB @1600)
 */
object SplitString {
  def split(string: String): (String, String) = {
    def loop(chars: List[Char], upper: String, lower: String): (String, String) =
      chars match {
        case Nil => (upper, lower)
        case char :: remainChars =>
          if (char.isLower) loop(remainChars, upper, lower + char)
          else loop(remainChars, upper + char, lower)
      }
    loop(string.toList, "", "")
  }

  val (upper, lower) = split("HelloWorld")
  println(upper + lower)

  def benchmark =
    for (_ <- 1 to 1000 * 1000) { split("HelloWorld") }

  benchmark
}

split can be implemented with partition of List.

object SplitString {
  def split(string: String): (String, String) = {
    val (upper, lower) = string.toList.partition(c => c.isUpper)
    (upper.mkString, lower.mkString)
  }

  val (upper, lower) = split("HelloWorld")
  println(upper + lower)

  def benchmark =
    for (_ <- 1 to 1000 * 1000) { split("HelloWorld") }

  benchmark
}

This took:
time scala -nc ~/new_split.scala 11.00s user 0.46s system 247% cpu 4.631 total
better result?