The 970 has been a great upgrade for me, coming from a GTX 760.
There are a few setting tweaks that I would recommend testing, such as turning down AA to 8x or lower,turning down shadow quality, reducing civ traffic and the "every frame" setting for cockpit displays.
I plan on upgrading to 6gb card myself, the only performance issues I encounter are slow downs usually caused by a lot of units on screen at once.
Tweaking is necessary to achieve the optimal performance/quality you are used to. Sometimes however performance is compromised another factor, I hope you are able get it pinned down. Like everyone says, DCS 2.0 is around the corner.