My setup is 2.66 i5, 8GB and 4850 and I get 40 fps in 1900 mode. 20 fps in 2560 mode. Settings are default, but a couple options bumped up for better detail. Even though the requirements say iMacs are only supported back to 2010, this 2009 model works fine since the high-end 27" model has a better video card than the 2009 21".