How to speed up access to the RichTextBox Lines property

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private void Form1_Load(object sender, System.EventArgs e)
{
    Cursor.Current = Cursors.WaitCursor;

    StringBuilder Buffer = new StringBuilder("");

    for (int i = 1; i <= 1000; i++)
    {
        if (i > 1)
        {
            Buffer.Append(Environment.NewLine);
        }

        Buffer.Append("This is line number " + i.ToString());
    }

    TheRichTextBox.Text = Buffer.ToString();

    Cursor.Current = Cursors.Arrow;
}

private void ForLoopButton_Click(object sender, System.EventArgs e)
{
    Cursor.Current = Cursors.WaitCursor;
    int Len = 0;

    int Start = Environment.TickCount;

    for (int i = 0; i < TheRichTextBox.Lines.Length; i++)
    {
        Len += TheRichTextBox.Lines[i].Length;
    }

    int ElapsedTime = Environment.TickCount - Start;

    ResultsTextBox.Clear();

    ResultsTextBox.Text = "for loop Elapsed time = " + ((double) ElapsedTime / (double) 1000.0).ToString() + " seconds Result = " + Len.ToString();

    Cursor.Current = Cursors.Arrow;
}

private void ForEachLoopButton_Click(object sender, System.EventArgs e)
{
    Cursor.Current = Cursors.WaitCursor;
    int Len = 0;

    int Start = Environment.TickCount;

    foreach (String Line in TheRichTextBox.Lines)
    {
        Len += Line.Length;
    }

    int ElapsedTime = Environment.TickCount - Start;

    ResultsTextBox.Clear();

    ResultsTextBox.Text = "foreach loop Elapsed time = " + ((double) ElapsedTime / (double) 1000.0).ToString() + " seconds Result = " + Len.ToString();

    Cursor.Current = Cursors.Arrow;
}
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