I don't know how relevant you'll find this but I have a first-generation 2.66 GHz Mac Pro, upgraded with 8 cores, 12 GB of RAM and an Apple-branded 1GB Radeon HD5770.
I bought the Steam version of Civ 5. It runs great at the start of the game but, on medium to large maps, once the game gets to around turn 250 or so, I experience severe slow-downs while scrolling around the map as well as graphical corruption in the form of grey areas, red and white checkerboards and very slow re-draws.
I've tried trashing the prefs. I've tried running windowed. I get the same problems whether my resolution is 1920x1200 or 1600x1000 or 1280x800. I also get the same problem whether I use the default settings or I turn all the video options to their minimum settings (or their maximum, come to that!).
On my system, which exceeds Aspyr's recommended system requirements comfortably, I consider the game to be frustratingly unplayable under OS X.
However, when I boot to Windows 7 and play, then the game starts and runs just fine with all the video settings to their maximum values. By the later stages of the game, the graphics do slow down a little, but it is still playable and enjoyable.
I've been in touch with Aspyr's tech support and sent them the log files they requested. They've not been able to suggest any fixes beyond what I've already tried but they said there is a patch due around the end of August. I'll try that when it arrives but I'm not holding out much hope.
For now, as much as I dislike it, I'll boot windows 7 in order to play Civ 5.
