The bitrate is pretty much your quality setting , the higher the bitrate the better the picture . Another option if your cpu is good enough is the "x264 cpu preset" the LOWER you set it the more cpu power it will use to encode the video before it goes out, thus raising the picture quality.
so for example a 720p 30fps stream with a medium preset and 1000bitrate would have much better quality than the same settings but with a very fast preset.
what also helps is to play the game in the same resolution you are streaming at , since you don't need to downscale it. Also lowering the audio bitrate helps since this also uses resources of your max bitrate settings.
But like i said it is VERY demanding and not recommended to set it anything lower than fast on a 1 pc setup.
But in your case i would recommend leaving the cpu preset on very fast since your cpu is not really strong enough to handle a lower preset . So if you can't use a higher bitrate you can't do more to improve your quality.
There are only 3 options , get better internet with a higher upload speed , a stronger cpu or a second pc to stream from allowing you to lower the preset.
