Okay, so that is a very small resolution to play at, all things considered. You will get VERY high framerate from the GPU, so you will absolutely run into a bottleneck. How bad? It's hard to say.
This is what I recommend, if you get the GTX 970, first order of business is to upgrade your monitor to take advantage of all that graphics power. Second would be to upgrade your CPU.
Alternately, you could keep your current monitor, spring for a cheaper GPU (R9 270 or 280/5) and upgrade your CPU with the difference. You wouldn't notice the weaker GPU at your current resolution, especially with the CPU bottleneck.
That's a tough call.