http://forum.insanelymac.com/index.php?showtopic=91755

Here's my tutorial over at insanelymac for running this card with GFX-EFI strings. Try it out from start to finish, and if you still have sluggish performance, that's just the way it runs. IMO this card runs good, but I'll be the first to say it needs some more optimizing from Apple to reach full potential. It doesn't run in OSX as well as it does in Windows. That's just the nature of the beast.