Originally Posted by robotbob
please consider getting a separate power supply just for your card. you mac pro is working but it cant handle it long term. what it will eventually do is fry your logic board. Search thru links on macrumors forums posted by a user called macvidcards. he is tight with nektas ( who was showing folk how to hack the cards in macpros before it was easy with mountain lion.
Note that while the GTX 480 and GTX 580 technically work, they have a TDP of 245-250W which is above what the Mac Pro can officially support (225W). If you want to use these cards, you'll probably have to drive them with an external power supply. In general, a card like the GTX 570 would be a better choice, since it has a TDP of 219W.
hope that helps
I have asked quite some people about that fact...
The ones, who are working at a Mac Service Center say, that the Mac can handle the card I have.
There are actually two type of cards of the 580's: the GTX580 with 1.5GB and the GTX 580 with 3GB. The 3GB version needs an additional power supply for sure, but not the one I own (1.5GB). I run the card since August 2012 in my Mac Pro 3,1 (early 2008) and it does a good job. The Mac people said, I should have no worries about damaging my Mac Pro.