The max the ingests are rated to handle without issues is 3500kbps, partner or no.
(You technically can go past this, but it's "here there be dragons" territory, full of buffering and the potential to get banned as a potential DoS attack.)
Twitch released usage metrics a while back that showed that a majority of viewers are able to watch smoothly at 2000kbps. Going above this (even to 2500) causes an increasing portion of the viewer base to start to buffer. 3500 is solidly into 'buffering hell' territory for many, unless you're a Partner and so have transcodes available (which are lower bitrate versions of your stream).
The tricky bit is, a number of people will say to just run at 3500kbps, that they never see buffering or hear any complaints. They ignore that they are in the minority of viewers, and that they don't hear complaints because people just joining a stream and buffering a bunch won't complain... they'll just leave. Usually without saying a word. They also don't understand why they can't get or keep viewers.