If were talking strictly from a resolution standpoint my GTX970 can power everything on Ultra on 1440p. The worst is on planets when I drop to between 50-55fps. The DK2 has a resolution of 2160x1200 or 1080x1200 per eye meaning it technically has less resolution than true 1440p. Going off of this the 970 should be more than enough card to power the DK2 in elite dangerous.
A 970 might be ok for a DK2 - it was with SDK 0.5, prior to Horizons - but CV1 has higher requirements. The resolution you quoted is for CV1 (DK2 is 1920x1080) but there are a couple of things you didn't consider. First is that the render target (the resolution that the frame is rendered in prior to being distorted for display) is higher than the screen resolution, about 4.3 million pixels rather than the 2.6 million pixels of the screen. The second is that the CV1 is 90Hz while you are presumably running your 1440p display at 60Hz. Including those factors in the calculation shows that CV1 requires about 400 million pixels per second which is much higher than the 220 million pixels per second that 1440p requires. And remember that while a drop in framerate is often acceptable on a monitor, it is not in VR so while a 1440p display only really requires an
average of 220 Mpixels/s, a CV1 requires a
minimum of 400 Mpixels/s.
TL;DR: The CV1 requirements are actually much closer to 2160p than 1440p, and about double the requirements of a DK2. A 970 certainly won't be enough for ultra on CV1 and might suffer framerate drops even on minimum settings.