I had some files created in Excel 2002 (Office XP) which I was using in Excel
2003 without any problems. These files consist of 1 worksheet and around 30
chart sheets. The data worksheet contains 7 columns of raw data,
approximately 20 columns of data computed using formulae and approximately
4000 - 5000 rows. Some columns of the raw data and the computed data are
plotted in various charts.

I've recently upgraded from Excel 2003 to Excel 2007. In Excel 2003, I was
not facing any problems in modifying the charts. However, in Excel 2007 it
takes anywhere between 2 - 7 minutes to simply select a data series and a
similar amount of time apply simple formatting (like reducing the marker
size). This problem persists even after saving the file into 2007 format
(xlsx).

Any suggestions?

Thanks and Regards.