There are no 'best settings', due to the number of variables involved with a livestreaming setup. Just starting points which you have to test from, based on trial and error.
That said, your CPU is extremely weak; it's a budget machine special. Real time video encoding (and by extension livestreaming) is extremely CPU-intensive. It isn't going to be able to handle much.
Try running 320p@30fps, Superfast preset, with 1000-2000kbps dependent on your connection speed and stability.
You may need to downscale further, to 240p, depending on which game you are playing.