VBA Delete Multiple Worksheets

I have a workbook that users add sheets to, and save and the workbook just get's junked up. I know you can use VBA to delete a sheet, just by simply executing

For Each ws In ActiveWorkbook.Worksheets
  ws.Delete
Next ws

But that is slow! What I am after is to delete ANY sheet that is not named "Master Data" or "Holding Pattern" in the workbook.