currently modded skyrim can is by far the most vram demanding game ever made. far behind that, crysis 3 with everything cranked up does indeed pass the 2gb vram barrier running at 1080p. other those two games, im not aware of any current games that will cross the 2gb vram threshold running at 1080p.
although, i would expect the frostbite 3 engine that will power battlefield 4 will more than likely cross the 2gb vram when played in 64 player multiplayer and all the settings maxed out. battlefield 3 already will push as high as 1.8gb and thats frostbite 2.
i would say get the highest vram you can. 1440p monitors will be dropping in price considerably in the next year. dont worry about 4k monitors, even 2 6gb titans cant run crysis 3 maxed out at 4k.
there is one user over on nexus mod forums running an nec 4k 40" monitors with two titans and a full s.t.e.p. mod installation on skryim. he gets very playable frame rates for about 5 minutes until fps drop then he crashes to desktop from hitting the 6gb vram cap.