Looks like that GT120 is an OEM MAC part correct? If you have this card and can upgrade the card, do it. It looks like it's selling for $150 on Apples site, which is at least $100 more than what it's performace is worth. If you are about to buy it, don't. It's a 2009 part, based on a mainstream video chip, I would not buy it used for more than $25 or 30. A new $70 card will be 3-4 times faster than this.
I have pretty much 0 experience with MACs but something has to be better than this for one. It will run WoW, maybe even at decent frame-rates at lower settings. But is really really really not worth the 150 Apple is charging.