I don't know much about Oculus Rift, but it's requirements can be found here:
https://www.oculus.com/en-us/blog/t...pc-sdk-0-6-released-and-mobile-vr-jam-voting/
"
On the raw rendering costs: a traditional 1080p game at 60Hz requires 124 million shaded pixels per second. In contrast, the Rift runs at 2160×1200 at 90Hz split over dual displays, consuming 233 million pixels per second. At the default eye-target scale, the Rift’s rendering requirements go much higher: around 400 million shaded pixels per second. This means that by raw rendering costs alone, a VR game will require approximately 3x the GPU power of 1080p rendering."
Based on the above, you might be able to use 2 x GTX 960s in SLI mode, but I'd wait till someone tests that before spending the cash. I tend to stay with singe card solutions, although I have friends running SLI no problem. For SLI you have to have the right motherboard, the cards need to fit in the case and power supply and heat becomes an issue.
In my limited experience, I've found video cards come down ~25% just as the new technology rolls-out and then discounted as low as 40% as it approached EOL. Your chart is interesting, but the 980 is still current technology so it would be more interesting to see a similar chart for a 770 which I couldn't find on the site.
As long as you are not overclocking, have a single GPU and the case itself has adequate fans, heat shouldn't be a problem. You can monitor temperatures using a variety of utilities including: GPU-Z,
http://openhardwaremonitor.org/, or the software from your video card vendor