I have 2 x 980Ti's and as ther others have said it's largely useless in VR. I've actually had to disable it entirely for certain games like project cars where it causes severe ghosting.
Shame, the NVidia VR works stuff where one card can do each eye sounds eyedeal (gettit?!?) but I don't expect to see it any time soon. In the mean time though a single hydrocopper 980ti boosting to a little over 1500mhz seems to be handling VR pretty well, especially since the ASW was implemented.
I would echo what the others are saying - at the very least wait for the 1080ti, and perhaps it's even worth waiting for the next generation unless you absolutely must have the latest and greatest. The 980Ti will serve you ok for a while yet, and if they do ever get off their arses and start using SLI VR properly then the pair will sing.