Excel絶対Withステートメントを使うべきです

絶対Withステートメントを使うべきです
http://officetanaka.net/excel/vba/speed/s4.htm

オブジェクト型変数に格納

Sub Test3()
    Dim i As Integer, j As Integer, myCell As Range
    Set myCell = ActiveWorkbook.Worksheets(1).Range("A1")
    For i = 1 To 300
        For j = 1 To 10
                myCell.Value = myCell.Value + j
        Next j
    Next i
End Sub