i cant max watch dogs just fine at both 1080 and 1440 on my 780 6gb. is not a GPU horse power issue some ppl with high end GPUs are having is not having enough VRAM on the card.
Yes it's the VRAM that's the issue, If I was building new now I would be going for the most because it's good to have it, May or may not be the trend, we just don't know right now, BUT if it is and you didn't go for the extra then you'll be mad.
The game isn't bad, and actually it was specifically developed for the PC as Ubisoft said they would be doing for this generation quite a while back. The real problem is people aren't realizing that the Ultra textures says 3GB for a reason, and 8xMSAA says 2GB for a reason too. You need a heavy amount of AA to really properly play this game.
The shadows also play a huge role and once those get patched to perfection we won't be seeing too many FPS issues on higher end cards. People have to realize the game just came out like a week or so ago and if you turn certain settings down just a bit you'll be butter smooth.