I have a 2010 iMac 27 inch 2.93GHz Intel core i7 with 12GB RAM.
it was built to order, with an internal Apple SSD 256GB and an internal 2TB hard disc.
The graphics is ATi Radeon HD 5750 1GB RAM
I have boot camp set up on the internal hard disk
I have win 7 on bootcamp.
I have the Mac Civ V on the SSD.
there is no doubt in my mind that the better Civ V is on boot camp and that is using the normal (slower)HDisc !
I can run Civ V at full resolution max everything with loads of mods on the steam install on bootcamp.
On the mac, despite using the fast SSD, I can only run Civ V at reduced screen size and at medium or low settings and with fewer mods. If I try higher settings or more mods, then Civ V runs out of memory after a few turns and crashes.
your experience may vary