If you're non-partnered, the 'golden point' is 720p, 30fps, 2000kbps.
You can start from there and test, lowering the h264 encoder preset one step at a time and testing for at least 10-20 minutes of live streaming each step, keeping an eye on your CPU temp with CoreTemp or similar, as well as your CPU throttling so it doesn't get too hot or throttle itself. Slower you go, better the stream will look without adding more bitrate.
Also, good luck starting out with League. It's a very super-saturated game, which means that getting any viewers at all starting out will be a matter of outright luck, someone finding their way to your stream amid the thousand other 0-2 viewer League streams live at any time of the day.
