I´d stick with that card for a while more, it´s a good card and upgrading it for non 4k play won´t translate into much of an upgrade really in price/performance ratio.
If you insist anyways. I´d take a look at the GTX 970 ($300), which is a good overclocker and a step above the one you got now. You could consider another R9 290 with crossfire alternatively.
GTX 980 TI is a bit overkill and around $600, however the fastest card around (not considering Titan X) and the extra vram it offers is nice as well.