A cap card will not improve your quality at all, in a single-PC setup. It will not lower your CPU/GPU usage at all. If anything, it will raise your overhead and increase load when using one with OBS, if gaming on the same machine.
That's bad/misleading information that Avermedia has been putting out for a long time now, as they sell low-end cap cards and tend to prey on newbies.
You are trying to stream 1080p@60fps video on 2000kbps.
That isn't going to work, full-stop, and will look terrible.
Downscale to 720p, and 30fps. That will fit in a 2000kbps bitrate budget.
To run 1080@60 you would need to use at least 5000-6000kbps, which almost no one on Twitch would be able to watch without buffering constantly, as a non-partnered stream. Even running 1080@30 needs 3000kbps as a bare minimum (and wants 3500+), and a very small segment of users can watch that smoothly. Your channel would be exceedingly unlikely to gain any realistic viewership.
Downscale and drop your fps rate to work within the realistic 2000kbps limit. It will look a lot better. Not perfect, but a vast improvement over what you're putting out now.
720p@30fps, 2000kbps, x264 Veryfast (or lower, based on live testing, and keeping at or below 80% CPU load; your 6700k could probably at least do Medium which will be a marked quality improvement over Veryfast).
