Upgrade from Excel 2007 to Office 365: Excel very slow

I have recently upgraded from Excel 2007 to Office 365.

I am finding that as soon as I have a few workbooks open (let us say 6 workbooks of 2MB open without many calculations) or one medium workbook (with lots of calculations - let's say a 15MB that takes 30 seconds to calculate) that I am having problems jumping from one cell to another - even within one worksheet, just to the adjacent cell.

For instance if I am in cell E40, just moving to cell D40 using the arrow key can take 5 seconds.

This is so frustrating, that I just simply use Excel 2007 for anything other than small workbooks.

I have tried the following, but have had no success:

1. Disable animations using the registry
2. Excel Options/Advanced/Disable hardware graphics acceleration
3. Disable addins
4. Looking at Microsoft's help to see if there is anything pertinent (there doesn't seem to be)