http://forums.overclockers.co.uk/showthread.php?t=18444958
I don't have your resolution so I can't be entirely accurate but my resolution is more pixels.
To be honest as you play Skyrim so much then it is clearly worth it for you I would go with the 4GB. As you say, you don't want to be VRAM limited and you can even be VRAM limited depending on the mods at 1920*1080 so it would be worthwhile for you personally.
I was just getting the point across that unless you play Skyrim 'a lot' then it probably isn't worth it although to you I would say it is worth it. The problem with being VRAM limited is it's a wall: there's no slight slowdown or mild FPS drops; it's single digit slideshow time and what's worse is it's not even consistently slow. It will hit max FPS and then all of a sudden just freeze. It's not good!