I have an 2008 mac pro 3,1 8 core with dual 2.8ghz Xeons. 6gb ram and I just installed a gtx 570 to replace my 2600xt. I'm still getting poor performance. I know that the cpu has more to do then the video card but I am still only able to get good framerates at fair settings anything above that will drop the frame rates below 25 fps and ultra to below 20fps. Is this what I should be expecting? I know my system is fairly old but I thought that the dual xeon would be able to give me good performance paired with the gtx 570.