That's 4285.71428571kbps, using the same lowercase b that you did and correcting the second error below. That's towards the low end of some of our own streams. Are you having any other problems?
Bytes are uppercase B
Bits are lowercase b
The difference is a factor of 8, which is a lot, so my answer could be way off. Garbage in, garbage out.
To be even more pedantic:
Lowercase m means milli, or 1/1,000
Uppercase M means mega, or 1,000,000
So...what quantity are you describing again? :-)