Yes buying on Steam let's you play on PC or Mac. My PC is nothing special but it's really just the dedicated graphics card that makes the difference. Still can't run on high or ultra but I'm fairly confident I'll stat around 30 fps, even late game.The performance is not as big of a deal if the Steam deal lets you play on either Mac or PC. Were you able to try on PC? If it works I can use the MBP only for "emergency" Civ sessions.
The MBP will work for emergency sessions (lol). Again my only concern is overheating.