You know, this is a great idea for a challenge! I might try to make a small population town that also uses a fair bit of the map... like one of those rural towns where your closest neighbor is half a mile away.
The Mac version in my experience is not anywhere near par with the Windows version. I run both (Mac version and Windows version in Boot Camp) on the same machine and I can do mid-to-high graphics on Windows while the Mac version has to have everything minimized in order to run smoothly.
You do get both versions when you buy the game though. So you can try it out either way. Boot Camp + Windows version works great for me.