You want your bit rate to be about half of your upload.
Because it will occasionally spike to twice what you set it to.

I've got 50/5 (up/down) Mb/sec.
Which on speedtest.net usually shows 45-48 Mb/sec (download) and 4.75-4.90 Mb/sec (upload).
I've found a 1,400 bit rate is good, in that the "test connection" (for XSplit) always comes up "green" which means no packets dropped (audio is another 96, for a total of just under 1,500... which is quite a ways below my 4.75-4.90 up speed).
The higher the bit rate, the better the quality... but only if the viewer can handle it, and setting the value too high will kill the quality for anyone whose system cannot process it quickly enough.