You need a better CPU. i5s generally run out of gas after 720p@30fps.
If you are streaming to Twitch though, exceeding 2000kbps is NOT recommended. 60fps is unnecessary, and mostly a waste of bitrate if you are not a partnered caster. There's a big difference between playing a game at 30fps vs 60fps. Streaming, not so much. Especially when it comes down to the balancing act of providing good quality while keeping your bitrate low to reduce buffering and remain watchable.
3000kbps will cause a large portion of potential viewers to buffer, and leave for another channel. And with an already super-saturated game, if you want your channel to have a chance to grow, you need to be as accessible as possible.
OBS uses the GPU for scaling, compositing, and some other back-end functions, but uses less than 1% of its capacity. You can use NVENC to encode on the card, but the quality is trash at streaming bitrates, and is not a realistic option.