It is actually possible from 4.1.x already.
Also see documentation for the -speed switch.
Sorry to dig up such an old thread, but that's the top result from Google, so others might find it useful as well...
I read the documentation, but there are 2 conflictual informations:
In the "Switch" column the unit is kbps, and in the description column, KB/s.
Same on the "Synchronize" command page.
Which one is it ? kb (kilobits) or kB (kiloBytes) ?
Thanks for your answer.