I'm currently running 2x1080p 24" 144Hz monitors so I guess I'm covered.
Wait, do you game on one monitor and do other things on the other monitor, or are you gaming across both screens (effectively playing the games at 3840x1080)?
If only on one, you're fine. The 1070 was generally a high-to-max details at 2560x1440 @ 60fps card. So, for a lot of modern games, it's probably good for around 90-100 fps (that's a VERY rough estimate) on a single 1920x1080 monitor. More if you're not maxing out the details.
If you do notice any performance issues, it's possible the CPU is holding you back, depending on the game.
Oh, and Ashes of the Singularity - that brutalizes all video cards.
Generally, though, if things play fine, enjoy your system. When you start noticing performance issues, then start to track down why, and then maybe determine if a hardware upgrade is needed.
EDIT: or if your needs changed, as with the gaming-and-streaming scenario. Which I apparently didn't read all the way down this thread before answering . . whoops!