It depends on what resolution you're running. Years ago, 7680x1440 was only possible with two GTX Titans/780 Ti's if you even wanted to attempt to hit 60 fps. Most modern games can be played with a single GTX 1080 Ti now though there are still plenty of games that require two GTX 1080 Ti's just to hit 60 fps at nvidia surround resolutions. Once the 4k 144hz monitors hit the market, enthusiasts are going to have to adopt sli to even have any semblance of hope to reach the required fps. Personally, I have two FTW3's on preorder which gives me pause since I replaced my 7680x1440 set up with a lg c6 that's only 4k. I could probably get by with a single 1080 Ti, but there are plenty of games out there that will still require lowering settings to hit the magic 60 fps number.