Hi everyone, I have asked several people this question but have gotten mixed answers, so I thought I would make a whole thread to help narrow things down. I have a Mac Pro 1,1 with two cards. My main card is an ATI 2600XT (taken from a 2008 8-core Mac Pro), and the original GT 7300 for extra displays. I currently run Snow Leopard on my machine, but I wanted to load either Mtn. Lion, Mavericks, or POSSIBLY Yosemite on it, with one of those custom-install guides floating around on the internet. Many have successfully been able to install these operating systems on their unsupported Macs; HOWEVER, my 2600XT card is a little questionable. I have heard people say that anything past Snow Leopard on one is either finicky, slow, or both... I have also heard people say that it would be fine, considering a supported, older iMac with a lesser card can run any of these three operating systems just fine. So, what do you guys think? I am guessing the 7300 is out of the question, but what about my 2600XT? Would things run fine or what? Is it not really about ability but rather compatibility? Are there any out there who have had experience with running one of these operating systems in a Mac Pro that has this card? Thanks, MDD P.S. If this card isn't good for any of this, what card can you all recommend? I'd be looking for something easy on the wallet, yet not cheap and underpowered.