Im thinking of getting a new video card. As some of you may know, i use a iMac mid 2011 running Mac OS X Lion. It has an AMD Radeon HD 6750 512 MB video card. Well long story short, i suck at choosing things. So i was wondering if any of you know any good video cards that are compatible with my iMac. I was thinking about a AMD Radeon HD 6850 but i am skeptic about it.