lower game graphic settings that are directly related to the CPU and lower your stream quality settings.
Streaming uses a tone of CPU power.
First, OBS uses CPU to just run, then, it uses even more CPU the more things you add to your scene and also the more complex each item is/the size of the item (such as overlays, gifs, webm, browser sources, etc.)
Next, it uses a bunch more CPU just to encode the stream and the amount of extra CPU it uses to encode depends on the quality settings you set it to.
You can try setting it to encode using NVENC at the Default quality setting and see if it helps by basically offloading the encoding part to the GPU NVENC Encoder chip of your GTX 1070.
But if using NVENC, you should expect to lower your game graphics a little bit so that you aren't putting a super heavy load on your GPU.