11-05-2013, 11:15 PM
I have just found this,
Mac System Requirements
OS: Mac OS X 10.6, 10.7, 10.8
Processor: Intel Core 1.8GHz+
Memory: 1 GB RAM
Graphics: NVidia GeForce 7300 GT ATI Radeon X1600 Intel GMA X3100 128MB VRAM
Network: Broadband Internet connection
Hard Drive: 3 GB available space
Additional Notes: OpenGL 2.0 compliant
So comparing that with your iMac specs only tells me that your iMac beats the minimum system requirements needed to operate the game.
Your ATI Radeon HD 5670 in comparison to the X1600 has pros and cons.
It is better than the X1600 but the X1600 has better memory bus for example.
I believe it would run on your iMac just in a lower resolution.
I hope this helps.