Personally I would go with keeping the 980 and getting the 1440p monitor as the 980 probably cost you a decent amount and there's no reason to replace such a card especially when the 980 Ti isn't a super huge step up from the 980. However if your goal is to game on very high settings, the 4GB of VRAM on the 980s will probably not suffice for 2K, so you should upgrade.