Example using XL2000, my 2.16MB file was saved as a 3.85MB file and took 45 seconds to save first time with Save As, and over one minute with subsequent Save.
The save time for this large file as a normal XL2000 file is 10 seconds. If you are saving as Microsoft Excel 97-2000 & 5.0/95 Workbook *you will see the following Microsoft Excel 5.0/7.0 saving on your status bar where you normally see Ready toward the end of the save then you are saving in multiple formats.
The journaling feature of Outlook logs many actions taking time from Excel, and eventually, the journal files become quite large, and performance is slowed.
The general recommendation in the Excel groups (and MS KB Q167081) is to turn journaling off.
Too much work to go into each folder, but I did find a lot more than I thought I had.