I believe that the mac and PC versions of excel contain significant differences in their base code and the way they work. I think the differences are more than just "optimization", they may have basic functional differences which mean that recalculation is handled entirely differently.

It also may be a question of configuration settings. Perhaps your installation of excel has something that is configured differently than the default. Can you check the sheet on someone else's Windows machine?

Another question: Is there any chance that the worksheet is referencing any external files, particularly if those files are on a network drive? Or are you opening the file directly from a network drive? Maybe the recalc slowness is a network access issue.