Most of us, if not all, have seen gpu's of the same model and/or specs but with different memory sizes. Whats up with this? Lets say i have "GPU X" having 512mb memory and "GPU Y" having 1gb memory and both of them are exactly the same exept the memory. Is there any significant improvement in performance from 512 to 1gb? If there are, in what ways can the 1gb version be better compared to the 512mb version?