I'm currently using a 5770 card with my Mac Pro 2,1 (10.7.5). It works pretty well, although I have recently started playing GTA V and, while the game does play, it doesn't play very well. The frame rate isn't usually too bad but as soon as weather starts (i.e. it rains) the graphics become very glitchy and there are other problems too, such as when looking inside a building outward, there are weird lines of blocks that appear, presumably from texture glitching or something. Strangely enough, the game itself tells me I only have 512MB of VRAM, when I should have 1GB. Is there a card you would recommend that would be compatible with this model Mac that would be significantly more powerful? Ideally at least 2GB of VRAM and preferably less than $300 but I'm flexible. It's hard for me to figure out what will actually work on this computer. Thanks!