I replaced the 8800GT in my early 2008 3,1 Mac Pro yesterday with a 7950 Mac edition. Cant say it was really worth it for the differences I experienced in games. There were noticeable improvements in the games I tried and in the GUI but not enough that I think it justifies what I paid for this thing. I assume things are mostly CPU bound because games such as Starcraft 2 showed enormous gains where as Dirt 2 the difference was fairly minimal. It frustrates me so much that Apple seem disinclined to spend some time and money on improving the graphics subsystem in OS X, it really is quite poor.