I currently have 2 GTX 980's in SLI.
1 is ready for a trade-in in Oct, the other is ready some time next year.
I should get about $550 for each one.
My choices are:
1) trade-in the one for Oct and get a 1080GTX for about $150 extra. Do the same next year when the other one is due, but 1080GTX prices will probably go down by then.
2) Trade-in both in Oct and "lose" the extra time for the second one, but use the money towards a Titan X and spend about $150 more.
Rig is used primarily for gaming. Monitors are 23" running at 1920x1080. One of the monitors is 120Hz so that I can use my Nvidia 3D glasses (although I don't actually use them too often anymore).
Secondary use is for 3D artwork/rendering and relys on CUDA a lot.