Streaming on OBS causes in game stutters although FPS is fine

I've noticed that my CPU usage for league of legends jumps to 25% when I'm in game. I've enabled low spec, I've disabled the client when I'm in game, I've reinstalled the client, done the repair option, I've checked whether my game is optimized by Nvidia or the intel is interfering. No matter what I do my game stutters whenever I stream on OBS. My specs are a GTX 1070 graphics card with an intel i7 6700 processor. I've tried to fix this so many times that it's honestly becoming obsessive now. I'm starting to lose hope.

I'm trying to run it at 2500 bitrate downscaled to 1280 x 720 at 60 fps on Twitch. My game stutters in game with 25% cpu usage even when it's running on my graphics card. I'm confused, please please please help me.