As above, a single 970 is unfortunately just not power enough for that resolution.
A 970 is a perfect match for standard 1080p gaming, offering frame rates from 50-120 on most modern games on ultra-high settings.
Going up to 2560x1440p would reduce those frame rates by about 30% (speaking from experience), so down around 30-90.
So, I'd say you could expect frame rates only as high as 80-85 at 3440x1440, and an average about 40fps on games such as GTA:V, The Witcher 3 and Fallout 4.
Obviously, this means that the 100hz of the X34 would be wasted, and gaming at 30-40fps isn't what most people would call ideal.