The theory is that most VR games target the 970, as soon as you find yourself in the 10X bracket you should be all set. I was using my DK2 on a 660Ti+2600k just fine. I demoed the setup at work with a few games (mostly DiRT and NoLimits 2). Out of the 30 or so people that tried it, only one person felt uneasy.

One thing I'd definitely recommend you do before purchasing a VR setup is demoing it for a decent amount of time. If you're susceptible to VR sickness, that's $800 down the drain.