TIPS for better performance
1.Use nvenc driver instead of X264.
2.Use 720p or even lower resolution
3.Use 30 fps,you can even try 23fps
4.Use lower bitrate. Bitrate is needed for improved quality on fast moving objects,but if you just stream a video or a live poll,you can get away with less.Try 500 and add more if the quality is crap.
These are just tips to improve performance when using OBS ,streaming from multiple opened browsers will also slow down your PC.I suggest you use firefox over Chrome for better RAM management.