I have a Mac Pro 3,1 with an 8800gt in it. I've been thinking of upgrading to one of the newer ati/amd cards available, the 5770 and 5870. But the 5770 doesn't seem to have enough power over my 8800 to justify the $250 and the 5870 is a bit to pricey for me. If I run my 8800gt and a 5770 in my Mac, how will osx handle them? Will the gpu only handle applications running on the monitor plugged into them? Meaning if display 1 is running portal 2 and is plugged into my 8800, will only the 8800 process portal? Or does osx do a good job of dividing up the work between the gpu's? I realize that the Mac Pro doesn't support sli/xfire under osx, and it might not be a great idea to mix an nvidia and ati in the same machine. I'm just trying to get the most bang for my buck. I'd appreciate any help/links with more info about this. And apologies if this is already posted somewhere, kinda difficult topic to search for.