Need advice on my next upgrade

[cerebro]

So I like to play wow and overwatch, while I'm playing I usually have YouTube or twitch open on my second monitor. I can def feel a performance impact whenever I'm running it on my second monitor. Ideally I'd like a set up where I cant feel the difference between having YouTube running on my second monitor. Also whenever I'm om a loading screen in wow it freezes my video for a couple seconds.

What is the biggest upgrade I can do that will directly impact my problem?

Z270X Gaming 5
I5 7600K
16 Gb Ram
GTX 1080 SC
Main monitor: S2716DGR 27.0
Second Monitor: B326HUL 32-inch

[cerebro]

What if I buy another S2716DGR 27.0

[cerebro]

Your issues should disappear, if we are dealing with this specific bug, which you should be able to confirm. I've heard that running 2-3 high refresh displays from one card might make it idle at higher frequency and temperatures, so if that bothers you, it could be something that can happen.

Meanwhile you should try running the Dell at 120Hz and see if you still experience the performance drop/stuttering.

My thing is I don't wanna gimp myself on performance

[motorized]

I use vlc media player in always on top mode on the same monitor with no performance decrease, with a firefox addon called "Open in vlc" on click it opens vlc and starts the video.

[Kyocere]

What if I buy another S2716DGR 27.0

I use the same primary monitor but have the S2719DGF as my secondary. It is essentially the freesync version that also runs at 144hz. Even with both monitors at the same hz this issue occurs. It disappears when I disable Gsync on the primary monitor so I suspect Gsync is the culprit. Try turning it off on your end to see if the issue goes away.