That card won't be able to utilize any more than 2GB VRAM anyway, well technically it might be able to, but the GPU itself is not powerful enough to drive the quality settings that lead to more than 2GB VRAM usage. As in cranking up quality with that card will make game unplayable anyway 2GB or 4GB.
4GB would make more sense for SLI if it is even possible for 960.
But yeah, might as well wait two weeks for 4GB boards popping up.