Welcome to the club =)

I play on my iMac 27", one version old (with HD4850 instead of HD5750(?) as a graphic card), and I can run this game at full resolution (2560x1440) maintaining standard drawing quality, high background drawing, high shadows, high texture quality and standard texture filtering, and I can have some good 30-40 FPS which are decent.
Or else I just switch to 1920x1080 and add some Antialiasing to x4, and the game goes very good. Sure, if it had full Fullscreen support (included a way to keep the DirectX focused on the program even if focusing on the system) it could be better, but I'll stay like this.
Playing here is pretty great, considering that this computer is meant to be a working one for me, I'm kinda surprised =)