What's the difference between these two cards? What can the 4GD do that the 2GD can't do? Is it worth while to push the extra money into a 4GD? I'll run 2 screens at 1080P, and a 3rd screen not at HD. I'll also do quiet a bit of gaming on said card, thus, I'm thinking of going GTX 770. Will there be an ATI option that can match this GTX 770?