The upload speed on your internet should be around double what you plan to use to live stream, so you can comfortably use 50% of the speed. You can push this to up to 80% of your internet connection speed if need be.
For example, a 1,000 kbps connection would let you stream from 500 kbps all the way to 800kbps.
If you are streaming at more than half your connection speed, do not try to watch your own feed at the same time as that will exceed your internet’s capabilities.
Also, please keep in mind that other variables, such as being on a wireless network or a shared network, will reduce the amount of bitrate you can stream at. Using a hardwired internet connection is the best way to go for live streaming.