It all depends on the quality you want to stream. The upload speed of the connection should be around double what you plan to stream at (or 50%). You can push this all the way up to 80% of your internet connection speed.
So a 1,000kpbs connection would let you stream from 500kpbs 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.