There's no difference between saves created on a Mac and saves from Windows. If there were we'd be having trouble reading the Mac submissions, and we don't. Loading the GOTM 11 Contender start file took about 22 seconds on my system the first time I opened it. A similar Highlands game created on my Mac took about 10 seconds. There's virtually no difference in size between the two Civ4SavedGame files. I then quit and relaunched and loaded up the GOTM 11 start again, and this time it took about 10 seconds, and subsequent tests all take 10 seconds. So I don't know what took longer the first time, unless it's due to some caching effect.