Crysis 3 at 4k with 4xAA......
In the review it was stated that the 3 gb cards suffered from the odd freeze up where as the 4 gb cards did not. Even then you can see that the 3gb cards have a decent average meaning they were just about playable with 3gb. The other 2 games i ain't sure enough about but crysis 3 looks not to be even close to 4gb judging by the 3gb card results.
I am guessing not many people would be happy to run with these fps anyhow even on the 4 way systems. So dropping settings thus lowering vram would be needed. We don't have the grunt by the looks of it even on 4 way systems in this type of game so 4gb is enough.