Not a single game use 2gb on 1080p, nowadays you can perfectly play with 1gb in this resolution (a 1gb gtx460 well oc can run almost all games near maximum setting), but 512mo is over. The best choice is a 3gb card only because they have a better bandwith, thats why 7970 are better than a 680.
With Dolphin I think the only things that will limit you willl be the software and the processor, I think 1gb card should enough to run 1080p.
With Dolphin I think the only things that will limit you willl be the software and the processor, I think 1gb card should enough to run 1080p.