It's not a minimum requirement dude. They are offering an optional ultra-HD texture download. It doesn't even ship with the game normally. 6GB cards do exist at the ultra high end (via Titan, or 6gb 780 variants), but they are not common. Assuming we take this at face value (we don't have benchmarks yet, so it could easily be exaggerated), that would mean you think of this as a "nice to have" option for the next video card you get 2-3 years down the line when you play this again. It's a way to future proof the game. Like Ubserampling in Witcher 2, it's not supposed to be running on normal computers, not even fairly high end ones. It's for the future, or for ultra high end rigs that cost 2000 dollars or more.