コードは VBA であることに注意してください。
コピー/貼り付けを行う代わりに、範囲の内容 (配列) を変換します。
Option Explicit
Sub Tabulate(ByVal src As Range, ByVal splitSize As Integer, _
ByVal destRangeStart As Range)
Dim i As Integer
Dim rangeToCopy As Range
Dim rangeToPasteOver As Range
Set rangeToCopy = src
Set rangeToPasteOver = destRangeStart
Debug.Print Now
Application.ScreenUpdating = False
For i = 1 To src.Cells.Count Step splitSize
' rangeToCopy.Resize(splitSize).Copy
' rangeToPasteOver.PasteSpecial Transpose:=True
rangeToPasteOver.Resize(ColumnSize:=splitSize).Value = _
Transform2DArray(rangeToCopy.Resize(splitSize).Value)
Set rangeToCopy = rangeToCopy.Offset(splitSize)
Set rangeToPasteOver = rangeToPasteOver.Offset(1)
Next
Application.ScreenUpdating = True
Debug.Print Now
End Sub
Function Transform2DArray(ByVal src As Variant) As Variant
Dim returnValue As Variant
Dim rowCtr As Long
Dim colCtr As Long
Dim destColCtr As Long
Dim destRowCtr As Long
Dim lRows As Long
Dim uRows As Long
Dim lCols As Long
Dim uCols As Long
lRows = LBound(src, 1)
uRows = UBound(src, 1)
lCols = LBound(src, 2)
uCols = UBound(src, 2)
ReDim returnValue(lCols To uCols, lRows To uRows)
destRowCtr = lCols
For colCtr = lCols To uCols
destColCtr = lRows
For rowCtr = lRows To uRows
returnValue(destRowCtr, destColCtr) = src(rowCtr, colCtr)
destColCtr = destColCtr + 1
Next
destRowCtr = destRowCtr + 1
Next
Transform2DArray = returnValue
End Function