Boy, when I'm wrong, I'm wrong. I'm still trying to find my post in one of the many threads here, but I predicted only the higher-end GTX 980 Ti would drop, not so much the GTX 970. And I was wrong.
The GTX 970 4GiB GDDR5 is really dropping here in the US, and can be had for as little as US$175 after Mail-in-Rebate (MiR).
- http://dealnews.com/Asus-Ge-Force-GTX-9 ... 36160.html
- http://dealnews.com/Gigabyte-Ge-Force-G ... 36340.html
I do not recommend GTX 970 for VR -- not even Rift, and definitely not Vive at all -- but it's quite good for Horizons at 1080p, possibly even 1440p, depending.
The minimum for Rift is really the GTX 980 Ti or GTX 1070, and I'd recommend the GTX 1080 if you can afford it. I get 90fps on the GTX 980 Ti, but it drops to 75fps on some planets, and definitely 60fps or under in some rings. The benchmarks are showing the GTX 1070 no better, so I'd opt for the GTX 1080 if I didn't already have a GTX 980 Ti.