I'd get a used 1070, you already from Scania you can get decent frames in the one game you say you play and it's a minimal investment. I'm on 1080ti SLI 4K and upgraded to it from 980ti SLI three years ago. I found a single 1080ti insufficient going from 980ti SLI and don't think a single card of that class enough for 4K for many games. 1070 now then sell them both mid next year and buy a single card at a reasonable (hopefully) price that can handle 4k well.