it all depends of the game, if you are talking about far cry 4 , crysis 3 and battlefield then you should go sli but if you are talking about cs go , wow and lol you should be fine with a 770 or above, as for an example my 780 ti can do 90 fps at 1440p on the witcher 2 on high settings.Playing at 1440p and at 144hz as heavy demanding than doing 4k 60fps.