Hello All
I was pulling my hair out because of this problem, and was particularly annoyed because the older version of Excel runs fast, but of course it can't open the new .xlsx files. I wanted to upgrade because I also use Excel at work on a PC and I love the ribbon.
I have found the answer and it's pretty obvious when you think about it...
Turn off all the "Microsoft Knows Best" automatic checking that Excel (and Word and Powerpoint) do. Not just the font menu thing, but EVERYTHING in the preferences that does something "automatically".
The only thing I left on automatic was the "autosave" feature.
Now excel runs as fast as it's Windows counterpart.
Chris